Modern Concept Science and Technology 10

46 cl aS Sification of living t HingS Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 47h. Mushroom and fern belong to separate kingdoms but since they are in the same evolutionary tree, they must have some similarities. List any two of them.STEP44. Long questions a. Classify the following animals and write one characteristic of each. i. Earthworm ii. Spider iii. Amoeba iv. Sea Cucumberb. Describe the body structure of Coelenterata with the help of a diagram of hydra. c. Observe the given diagram and answer the following questions.organism A organism BIt can fly. It is aerial. It has hollow bones. It is viviparous. It can fly. It is aerial. It has hollow bones. It is oviparous. Classify the organism A. Even though these organisms belong to different classes, they are still grouped together in the phylum Chordata. The presence of which organ makes them chordates. If that organ changes into a vertebral column, which sub-phylum should these organisms be placed into? d. Let’s suppose we saw a creature in the water, how can we tell if it is either a Pisces, Amphibia or a Reptilia?e. Discuss the interrelationship between the classification of organisms and their evolution. Project WorkCollect different parts of any five monocots and dicots and attach them in a chart paper by placing them in a plastic bag.♦♦♦

48 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 49Key terms and terminologies of the unit1. Life-cycle : A lifecycle is the series of stages of life of an organism, beginning with life and ending with death.2. Nectar : Nectar is a sweet liquid found in flowers that contains fructose and glucose. 3. Royal jelly : Royal jelly is a nutritious secretion produced by the royal glands of the worker bees which contains water, proteins, sugars, amino acids, fatty acids and vitamins. 4. Apicology : Apicology is the branch of science which deals with the study of honey bees. It is also called Apiology and melittology. 5. Queen bee : The queen bee is the longest, largest female fertile bee in the hive. 6. Drones : The drones are medium-sized, hairy, fertile, blacker bees of the hive. 7. Worker bees : The smallest, infertile, female bees of the hive are called worker bees. 8. Nuptial flight : The flight of a queen bee followed by drones for reproduction is called nuptial flight. 9. Metamorphosis : The process in which an insect changes from an egg to a larva followed by pupa and adult to complete life-cycle is called metamorphosis. 10. Spermathecae : The sac where queen bees store collected sperm after mating flight is called spermathecae. 11. Moulting : The process in which the larva of the insect removes its outer layer of skin is called moulting. 12. Honeycomb : A honeycomb is a mass of hexagonal cells made by the worker bees using their wax. 13. Apiculture : The commercial rearing of bees is known as apiculture.Sequence of Curriculum Issued by CDC Lifecycle of honey bee Importance of honey beeUNITLife Cycle of Honey Bee 3Estimated teaching periods Theory Practical3 1Tej Kumar Shrestha, born on February 11, 1948, in Baglung, Nepal, was a revered figure in the realms of zoology and wildlife conservation. Throughout his life, he committed himself ardently to safeguarding Nepal's rich biodiversity. His extensive research, exemplified by seminal works like \"Wildlife of Nepal\" and \"Ichthyology of Nepal,\" left an indelible mark on our comprehension of Nepal's diverse fauna, securing his place as a revered naturalist and conservationist. Tej Kumar ShresthaAbout the Nepalese Scientist

48 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 49Introduction to lifecycleLiving things can give birth to young ones. After birth, they pass through the various stages of life. It is called lifecycle. A lifecycle is the series of stages of life of an organism, that begins from birth and ends on death. Some organisms are born directly and some are born through eggs. The life cycle of insects is unique. They show metamorphosis. The process which involves the egg, larva, pupa and adult to complete the lifecycle is called metamorphosis. Honey beeHoney bee is a social insect. The members of honey bee colony are extremely disciplined and industrious. They keep themselves busy all the time. Naturally, honey bees live in a special enclosed structure known as wild hive. Whereas some are domesticated in a place called apiary. Honeybees provide a wide range of benefits to humans. They produce honey, wax and other products. To make honey and wax, honey bees feed on nectar. Nectar is a sweet liquid found in flowers that contains fructose and glucose. Honey bees are the flying insects that belong to the arthropoda phylum. Apiology is the branch of science which deals with the study of honey bees. Study of bee is also called melittology. It is the branch of entomology (study of insects). Apis mellifera and Apis cerana are the two species of honey-producing bees known in Nepal.Structure of honey beei. The size of honey bees ranges from 9 mm to 20 mm.ii. Their bodies are divided into head, thorax and abdomen.iii. There are three segments in thorax and 9 segments in abdomen. iv. They have a pair of compound eyes and a pair of antennae.v. They have three pairs of jointed legs.vi. The type of skeleton present in honey bee is exoskeleton.vii. They undergo a complete metamorphosis. viii. The queens and workers have a stinger on the rear apex of their bodies for defence. Organization of the honey bee colonyThere are three types of bees in a honey bee colony. They are:i) The queen bee: A bee colony has a single queen that runs the whole hive. It is the only egg laying female in a bee colony.natural hive of bee in wild Honey bees in cellsMEMORY TIPSHoney bee is a social insect because it lives in a large wellorganized colony. Systematic classificationKingdom – AnimaliaPhylum – ArthropodaClass – InsectaGenus – ApisHoney beeThe venom gland is a gland containing poisonous chemicals and is located in the abdomen while the stinger is a sharp organ present at the rear end of the worker and queen bee.MEMORY TIPS

50 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 51ii) Drones: Drones are male honey bees. Their only job is to mate with the queen. They are very lazy. There are about five hundred drones in a colony.iii) Worker bees: Worker bees are sterile females that perform all the jobs in the hive. There are 20 thousand to 80 thousand worker bees in a colony.Queen bee The queen is the largest single fertile female bee in a honey bee colony. Its body is divided into head, thorax and abdomen. Its head is smaller than other bees. It has a shorter proboscis. Queen bees have smoother stingers with smaller barbs. It can sting more than once. Generally, it stings other queen bees. A diploid queen has 32 chromosomes in its cells. During the formation of gametes, a diploid cell divides into haploid cells with 16 chromosomes in each.The queen neither collects nectar nor does any other work but it can if required. Its main function is to lay eggs. The queen bee usually mates only once in her life and stores the sperms received from the drone in a sperm sack (i.e. spermathecae) in her abdomen throughout her life. A healthy queen can lay about 3000 eggs in a day. The queen bee lays eggs in the hive till she gets old, killed or lost. A healthy queen bee lives the longest in the hive i.e. 2 to 5 years. After that, a new queen is made by the workers. To make a queen bee, the worker bees feed a special liquid called royal jelly to the selected larva. The female larva which is continuously fed with the royal jelly turns into a queen. The queens and the workers are only different because of the difference in feeding.The queen bee runs the hive. It produces a number of different pheromones (i.e. characteristic scent or odour) from a gland near her jaw that attract other bees to her. Pheromones tell the other bees about the condition of the queen inside the hive. It is the scent of the queen that keeps the bees together in a swarm. The worker bees find their hives with the help of queen’s scent.Drone bees Drone bees are the fertile and haploid male bees. It means that they contain half number of chromosomes (16) in their cells. They are formed from the haploid eggs. This process is called parthenogenesis. Their number ranges from few to 500 in a hive. The body of the drones is divided into head, thorax and abdomen. They have larger head and eyes. Generally, these bees are very lazy and do not work. Their size is also smaller than the queen bee but larger than the worker bee. Their body is black and hairy. They do not have nectar gland, pollen sac, venom gland and stinger. Drones fly out with the queen to mate outside the hive. Usually several drones mate with a single queen. They die MEMORY TIPSThe pheromone produced by the queen bee attracts drones for mating. It also makes worker bees infertile. Queen beeA queen bee lays both diploid and haploid eggs. The diploid egg develops into either a worker bee or another queen. Both of these are female. While the haploid develops into a drone (male).MEMORY TIPSDrone beeDrone bees cannot eat nectar by themselves because they have very small proboscis and lack chewing parts in the mouth.MEMORY TIPS

50 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 51after mating. Their life span is generally about two months. Drone bees live temporarily in the hive either until mating with the queen or till the winter arrives. As they mate with the queen, they die because their penis and abdominal tissues are expelled along with the sperm. If winter approaches, they are expelled from the hive by the worker bees or are killed. Hence, the only function of the drones is to mate with the queen.FACTS WITH REASONSDrones die after mating. Drones die after mating because during mating the tissues in the abdomen tear apart. Worker bees The body of worker bees is divided into head, thorax and abdomen. Like other insects, they have 3 pairs of legs with hairs on them. The worker bees are structurally different from the queen bees and the drone bees. They are the smallest, infertile female bees in the bee hive. They live for almost 6 weeks to 6 months. A hive may have 20,000 to 80,000 workers.Workers gather pollen and nectar of flowers. To do so, they have mouth parts for chewing and lapping. Such mouth parts help them to collect the nectar easily. They store the nectar in their abdomen. Likewise, they have special hairs and sac like structures in their feet known as the pollen basket. They use these baskets to store pollen grains of the flowers. After collecting pollen grains and nectar, they carry them to the hive and store them in the hive to feed the larvae, queen and the drone. FACTS WITH REASONSWorker bees die after stinging, why? When a worker bee stings a person, it cannot pull the barbed stinger back out. It leaves behind not only the stinger, but also the part of its digestive tract, muscles and nerves. Due to this abdominal rupture the worker bees die after stinging. Why do worker bees collect nectar of flowers?The worker bees collect nectar because they convert nectar into honey and store it in the hive cells.FACTS WITH REASONSHow are the queen and worker bees similar and different?The queen bee and the worker bees are similar because both are diploid females with similar genes. They are develop from similar kinds of eggs. The only difference between them is that the queen is fertile and is fed with royal jelly but the workers are infertile and are fed with pollen and honey in their larval stages.Worker beeWorker bee collecting nectarIf a worker bee loses its pollen basket by any means, then it cannot collect pollen grains. So, it cannot help in pollination. So, agricultural production will decline. The forest ecosystem will be imbalanced. Bee cannot make bee bread. Larva cannot get to eat pollen grains. MEMORY TIPS

52 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 53Function of the worker beesThe worker bees are responsible for doing every work in the bee hive. Their functions are as follows:i. They collect nectar and pollen from the flowers to feed the larvae, queen and the drone. ii. They construct the bee hive. iii. They defend the other bees and protect the hive against the predators. iv. They feed and look after the larvae.v. They take care of the young bees (brood cells) and protect them.vi. Worker bees also maintain proper temperature of the bee hive.vii. They manufacture honey which is consumed both by bees and human beings.Comparison of the Queen, Drone and the Worker beesBasis of comparison Queen Drone WorkerSize Largest Medium SmallestStinger Present/ It can sting more than once Absent Present/ It can sting only onceLife span 2 to 5 yearsabout 2 months; dies after mating or in winter6 weeks to 6 months.Fertility Fertile Fertile Sterile FunctionLaying eggs and directing the worker beesMating with the queen and keeping hive warmConstructing the hive, feeding larvae, collecting nectar, etc.Number Usually one Up to 500 20,000 to 80,000 based on speciesInside the honey bee hiveThe honey bee hive is a natural waxy or artificial wooden structure. It acts as a home for honey bees. The natural hive is made up of wax which is produced by young worker bees. These worker bees produce sticky substance from their glands that become wax when they come in contact with air. The hive contains numerous hexagonal and cup-like structures called cells. These cells are the places where growth and development of the broods (young bees) occur. Hence, they are also called brooding cells. There are three kinds of cells present in a hive. They are drone cells, worker cells and the queen cells. The drone cells are larger in structure and is the home for the growth of drone bees. Similarly, the worker bees grow in worker cells which are smaller. The queen cells are extra-large and hanging downwards. These cells bear queens.Bees in the hive

52 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 53Life Cycle of Honey beeSimilar to other insects, the life cycle of the honey bee is also completed in four different stages. They are the adult, egg, larva and pupa. The process which involves the egg, larva, pupa and adult to complete the lifecycle is called metamorphosis. The life duration of the adult, egg, larva and pupa stages varies from species to species. The complete metamorphosis is observed in the life cycle of the honey bee. Complete metamorphosis means that all of the four stages of the life cycle such as egg, larva, pupa and adult stage are observed in the life cycle of the insect. i) Egg Honey bee eggs exhibit distinct characteristics. They are white and elongated, measuring between 1 mm to 1.5 mm in length. During the first day, the eggs stand upright in the cell, slant on the second day, and become parallel to the floor on the third day. The queen bee strategically lays eggs in separate cells for queens, drones, and workers. Larger cells foster queen bee development, while worker and drone cells produce their respective offspring. Fertilized eggs, containing 32 chromosomes, develop into female bees, while unfertilized eggs, with 16 chromosomes, give rise to drones. After three days, the eggs hatch into larvae, marking the beginning of their life cycle. ii) LarvaDuring the larval stage of a bee's life cycle, the caterpillar emerges from the egg, undergoing a distinctive developmental process. The duration of this stage varies among bee types, with queen bee larvae lasting 5.5 days, worker bee larvae enduring for 6 days, and drone bee larvae progressing over 7 days. Characterized as voracious feeders, bee larvae moult 4 to 5 times. The process in which larva shed their skin periodically is called moulting. Notably, the size of the larva destined to become a queen or drone is larger than that of a worker bee. Differentiation in diet plays a crucial role in their development. Larvae of various types are fed royal jelly for varying durations. The large female larva which becomes the queen bee eats royal jelly forever. The large male larva which becomes a drone bee starts eating a dilute mixture of Lifecycle of honeybeeThe number of eggs laid by the queen bee depends upon the species of bee. MEMORY TIPSFertilized eggs give birth to females and unfertilized eggs give birth to males. MEMORY TIPSRoyal jelly is a very nutritious secretion produced by the royal glands at the head of the worker bees. It contains water, proteins, sugars, amino acids, fatty acids and vitamins. MEMORY TIPSPollen bread (bee bread) is made from honey and pollen. The larvae for drone bees and worker bees are fed with pollen bread after 3 days. Adult worker bees and drone bees also eat bee bread. MEMORY TIPS

54 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 55nectar and pollen after three days of royal jelly intake. Small female larvae which become worker bees, consume royal jelly for three days and then shift to a diet comprising pollen grain, nectar, and bee bread. Farmers should be trained to harvest royal jelly.Farmers should be trained to harvest royal jelly because it can be sold for a good price in the market. It is sold for its nutritional and medicinal value. It is a good source of income for beekeepers. FACTS WITH REASONSiii) PupaThe duration of the pupa stage varies among bee types, with the queen bee pupa lasting for 7.5 days, the worker bee pupa enduring for 12 days, and the drone bee pupa progressing over 14 days. The pupa stage is marked by inactivity, as it neither feeds nor moves. During this stage, a fascinating process called histolysis takes place, where all the tissues of the larva dissolve into the fluid. The process in which the old tissue of the larva degenerates is called histolysis. Subsequently, the essential new organs and tissues needed for the adult bee's development are formed through histogenesis. Histogenesis is a process in which new organs are formed from the dissolved cells in the pupa stage. This transformative process involves the creation of new organs from the dissolved cells in the pupa, playing a crucial role in shaping the pupa into a mature bee.iv) AdultIn the adult stage, a honey bee's body is divided into three parts: the head, thorax, and abdomen. The thorax has three segments. Each segment has two legs. Therefore they have six legs. They have four wings. Two wings are in the first segment and another two wings are in the second segment of the thorax. They have paired compound eyes to see. It helps them to see in any direction without rotating. Anteena helps them to sense their surroundings. Their abdomen has 9 segments. Only the six segments are prominent in adult females. 7 segments are prominent in males. They breathe by tracheal tubes present in the thorax. There are three morphology of bees. They are queen bees the largest one, drone bees the medium-sized and worker bees the smallest one. Each bee type in the colony has its specific tasks. The queen bee the fertile female lays eggs and oversees the hive, while drones the male bees assist in fertilization. Worker bees, the infertile females have duties based on their age. They engage in activities like cleaning, nursing, honey production, and hive protection. The transition from an egg to an adult takes different durations for each bee type: the queen in 16 days, the worker bee in 21 days, and the drone bee in 24 days. Adult queens, workers, and drones exhibit distinct physical structures, appearances and functions.Figure: Different stages of honey bee

54 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 55Time taken by bees to complete their life cycleThe time taken by the queen, drones and the workers to complete their life cycle is given in the table below.Bee Eggs Larva Pupa Duration required to be an adult Average life spanQueen 3 days 5.5 days 7.5 days 16 days 2 to 5 years Worker 3 days 6 days 12 days 21 days 6 weeks to 6 monthsDrone 3 days 7 days 14 days 24 days about 2 monthsThe functions of various bees at their various stagesS.N. Type (caste) of bees Age Interval Functions or duties1 Drone bee Throughout their lifetime To mate with the queen and warm up the hive2 Queen bee Throughout their lifetimeTo lay eggsTo guide and unite the hive members by secreting a characteristic scent or odour. 3 Worker bee1-3 daysThese worker bees are small and do not perform many functions. So, they are also called baby worker bees. They provide warmth to the eggs, larvae and pupae. They learn to fly, move, eat and clean the hive. 3-6 days They eat a lot and also feed other larvae. 6 - 12 daysAt this age, the hypopharyngeal glands are developed and produce royal jelly. The worker bees of this age feed royal jelly to the larvae and the queen. 12-18 daysDuring this age, the hypopharyngeal glands become degenerated. Then, due to overfeeding of honey, 4 pairs of wax glands are regenerated in their abdomen. The workers of this age secrete a solid sticky substance called wax. They use wax to construct hives and seal brood cells. So, they are also called builders or constructors. 18-20 days The wax glands also get degenerated. Then, venom/poison glands and stingers are produced. The stingers help to attack other invaders and guard the hive. Only the queen and the workers have stingers. The queen uses its stinger to attack or defend itself against other queens. Similarly, the workers use the stingers to attack or defend against other insects and protect the hive. After 21 days They start to collect nectar, pollen, water, etc.

56 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 57Swarming If the queen bee is very old or dies or if there are too many bees in the hive, the workers make new queen bees by feeding royal jelly to a female larva forever. Sometimes two queen bees are formed in the hive. In this situation, one of the queen bees leaves a hive along with a few thousand worker bees. This process is called swarming. The event in which the old queen leaves the hive with lots of worker bees to create a new hive is called swarming. It occurs at noon. The honey making processHoney is a sweet substance produced by honey bees, containing around 80-85% carbohydrates, 15-17% water, 0.3% protein, and 0.2% amino acids, vitamins and other elements. Honey is manually made by bees. It is not produced from glands. It is a mixture of monosaccharides called fructose and glucose. To create honey, worker bees collect nectar from various flowers, covering long distances around the hive. The colour and flavour of honey depend on the flowers visited. Worker bees store the nectar in their abdomen's second stomach, where it combines with proteins and enzymes to turn into honey. The honey is then stored in hexagonal cells of the honeycomb, made by bees using wax. Worker bees continue collecting nectar and depositing honey until all cells are full. To thicken the honey, worker bees flap their wings over the comb, evaporating water from the honey. Uses of honey i. Honey is eaten to remove cough. ii. Honey is eaten as a good source of calories. iii. Honey can be used to make candies and cakes. iv. Honey can be used as an antiseptic. v. It can heal wounds.vi. It can be used as a food preservative. Advantages of honey beesHoneybees are really important for both people and nature. People raise them in a process called apiculture, mainly near crops with good nectar. This helps us get honey bee products like honey, wax, and royal jelly.Honey made by bees is sweet. We use it for eating and sometimes as medicine. Bees' teamwork is interesting for scientists. The wax from their hives is handy for making candles, paints and creams.Royal jelly from bees has health benefits, like helping with blood pressure and boosting the immune system. Bees also help in pollination while collecting nectar. They chose healthy plants for nectar. So, they help to spread pollen grains of healthy plants. This makes more and better-quality fruits and vegetables. Raising honey bees is a source of income for us. It also helps our country's economy. Comb honeyHoney bees live in the wild in forests, cliffs etc. They can make hives themselves. We do not need to make hives for them. However, if beekeepers make hives for them, bees stay in manmade hives too. Memory Tips

56 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 57Queen bees store sperm in spermathecae. Queen bees store sperm in spermathecae because the queen needs them for fertilization of eggs for many years.Beekeeping is a good alternative for farmers to earn money in Nepal. Beekeeping is a good alternative for farmers to earn money in Nepal because Nepal has lots of forests, crop fields and bee pastures. Honey can be sold for a handsome price. So, keeping bees would produce a profitable amount of honey.FACTS WITH REASONACTIVITY 1Visit beekeeping. Where are they kept? Ask beekeepers to teach you to identify three types of bees. HOT SKILL HIGHER ORDER THINKING SKILL1. The productivity of some crops increases if nearby farmers keep some bees in those areas.Honeybees choose the best and most healthy plants for gathering pollen. This helps cross-pollination of the flowers in a short period. As the parent crops are healthier and pollination is quicker, the productivity is increased, if nearby farmers keep some bees in those areas. 2. Differentiate between nuptial flight and swarming. The differences between nuptial flight and swarming are:SN Nuptial flight SN Swarming 1 The event in which a new queen bee flies out of the hive to mate with drones is called a nuptial flight. 1 The event in which the old queen leaves the hive with lots of worker bees to create a new hive is called swarming.2 It occurs when there are multiple queen bees in the hive. 2 It occurs when the new queen bee is ready for fertilization. 3. Drones are hatched from the unfertilized eggs of bees. Drones are hatched from unfertilized eggs because unfertilized eggs are haploid. Haploid cells can only change into drones in bees.4. Explain the relationship between beekeeping and agricultural production. The bees are the top pollinators in the ecosystem. They feed upon the nectar and pollen of the flowers. So, they travel from one flower to another for searching nectar. They transfer the pollen grain from one flower to another. They increase the rate of pollination. So, there will be more fruits on farms. They increase the rate of cross-pollination, which helps in the production of good-quality seeds. Bees like to eat nectar from healthy flowers from healthy plants so they spread pollens of healthy plants. It also helps to increase the agricultural production. Hence bee farming and agricultural production are interrelated. 5. Label the parts of the honey bee given in the figure alongside.A – headB – abdomenC – stingerABC

58 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 596. Bees are multipurpose insects. Bees are multipurpose insects because they help in pollination, honey production, wax production, the beekeeping industry, ecosystem and medicine use.7. Describe the life cycle of a worker bee.The life cycle of a worker bee starts with a fertilized egg. The egg hatches in three days. In the first three days, the worker bees learn to walk and clean the hive. On the third to the sixth day, they feed the larva. From the sixth to twelfth day, they produce royal jelly. From the twelfth to the eighteenth day, they secrete wax and make honey comb. From the eighteenth to the twentieth day, they protect the beehive. And from the age of 21 days, they go outside to collect nectar and pollengrain. 8. There is one egg in each brood cell. If only eggs A and B are fertilized, what will be the number of chromosomes in egg C? What happens if the larva from egg A is fed royal jelly for three days followed by pollen grains and bee bread? If only eggs A and B are fertilized then the egg C is not fertilized. Therefore, it is haploid and contains 16 chromosomes. If the larva from egg A is fed royal jelly for three days followed by pollen grains and bee bread the larva will change into a worker bee after metamorphosis. 9. Consumption of honey helps to reduce cough. What might be the reason? Honey is known for its anti-microbial and anti-inflammatory properties. These properties of honey prevents the spread of bacteria and reduce inflammation resulting reducing the cough. 10. Differentiate between drone bees and worker bees.The differences between drones and worker bees are:S.N. Drones S.N. Workers1. The drone has medium size. 1. The worker has the smallest size.2. Stinger is absent. 2. Stinger is present.3. Its lifespan is about 2 months. It dies after mating or in winter3. Its lifespan is of 6 weeks to 6 months.4. It is fertile. 4. It is sterile.5. Its works are mating with the queen and keeping the hive warm.5. Its works are constructing the hive, feeding larvae, collecting nectar, etc.6. Their number is up to 500 in a natural hive. 6. Their number ranges from 20,000 to 80,000 in a natural hive based on species.7. Drone bees are born from unfertilized eggs.7. Worker bees are born from fertilized eggs.8. There are 16 chromosomes in drone bees. 8. There are 32 chromosomes in worker bees.A B C

58 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 594 STEPS EXERCISE EXERCISESTEP11. Select the best answer from the given alternatives.a. Generally, how long is a bee?i. 1 cm to 2 cm ii. 9 mm to 20 mm iii. 9 cm to 20 cm iv. 9 segmentsb. What do honey bees feed upon?i. blood ii. juice from the stem of herbs iii. nectar and pollen iv. insects c. How many chromosomes are present in drone bees?i. 16 chromosomes ii. 16 pairs chromosomes ii. 32 chromosomes iv. 8 pairs d. Which larva will change into a drone bee?Feeds royal jelly only Feeds royal jelly, honey and pollen Small A CBig B Di. A ii. Biii. C iv. D e. What is the correct order of metamorphosis in a honey bee?i. larva, egg, pupa, adult ii. pupa, larva, adult, eggiii. egg, larva, pupa, adult iv. adult, larva, egg, pupa f. What are the functions of worker bees aged 12 to 17 days?i. feed and clean larva ii. produce royal jelly iii. make hive iv. collect nectar g. What are the features of the drone bee?i. furry, fertile, haploid ii. dark, wax glands, haploidiii. infertile, furry, diploid iv. fertile, diploid, furryh. Which bee is haploid? Bee A Bee B fertilization egg no fertilization i. A ii. Bee iii. B iv. A and B i. Which morphology of bee has the following features? Insect Fertility Duration of larva Duration of pupa Honey bee Seen 5.5 days 7.5 daysi. honey bee ii. drone bee iii. queen bee iv. worker bee

60 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 61j. Bee sting hurt and swell. Why?i. Its venom contains formic acid and protein.ii. Bee sting does not hurt or swell.iii. Its venom contains water that causes swelling.iv. It causes infection so it hurts and swells.a. ii b. iii c. i d. iv e. iii f. iii g. i h. iii i. iii j. iAns of MCQSTEP22. Very short questions a. If an egg is vertical in the brood cell, how old is it?b. Study the given statements and arguments. Comment who is right or wrong.Utshav: Beekeepers kill old queen bees, if there are two queen bees in the hive.Sampanna: I agree because two queens release two pheromones. The bees will get confused and fight.Susan: I disagree! We do not need to kill the queen. Two queens will work together, divide work and run the colony well.c. Which stage of the life cycle of a bee is shown in the diagram? d. Agricultural production increases if there are bees nearby. Give reason. e. At what age do worker bees keep the hive clean? f. In which condition does a group of honeybees separate from the colony to make a new hive? g. Write a difference between the larva of the drone and the larva of the worker bee. h. What a worker bee cannot do if it loses its pollen basket? Write any two. i. Sometimes we can see that many bees from different hives are fighting with each other. How do they know friends and enemies?STEP33. Short questions a. Bee farmers should kill a queen bee if multiple queen bees are found in the bee hive. How is it beneficial? b. There is a popular saying that human beings might go extinct if the bees go extinct. Put forward your opinion in favour of the statement. c. Write the difference between A and B.d. Let’s suppose there are two eggs of the bee. If the first one hatches into a male and the second one hatches into a female, which one is fertilized and how many chromosomes does it have?

60 life cycle of Honey Bee Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 61e. Ramesh used contact pesticides in a mustard field. The bees in the hive died. His mustard harvest also declined significantly. Relate the events. f. Write a short note on worker bees. g. The life cycle of a bee has complete metamorphosis. What does it mean? h. Which organs are formed during the pupal stage of the bee? STEP44. Long questions a. Describe the structure of the queen bee along with its diagram. b. Describe the life cycle of worker bees. c. How is the sex of the bee determined? Describe. d. If bees are social insects, what can we learn from them? How does beekeeping play an important role in the economy of Nepal? e. Observe the given concept map and answer the following questions. What are the consequences if bee A dies in the hive? Write two possible scenarios. Which one of them is an infertile female? What is the name of the process that gives birth to bee C? Egg of beeABCfertilization, feeds on royal jelly onlyfertilization, feed on royal jelly and nectarno fertilization, feed on royal jelly and nectarProject WorkVisit an apiculture farm and observe the following:i. Construction of the hiveii. Structure of the different beesiii. Extraction of honeyAlso, make different groups of students and prepare reports along with neat and labelled diagrams.♦♦♦

62 H eRedity Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 63HeredityUnit4CellNucleusChromosomeFatherXYXXDaughter Son Daughter SonXY XX XYMotherXX

62 H eRedity Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 63Key terms and terminologies of the unit1. Cell : The fundamental, structural, and functional unit of life is called the cell. 2. Cell division : The process in which a mother cell divides into two or four daughter cells is called cell division.3. Mitosis : Mitosis is an equational division in which a mother cell divides into two identical daughter cells. 4. Meiosis : Meiosis is the reduction division of a diploid (2n) parent cell into four haploid (n) daughter cells. 5. DNA : DNA is a double-stranded nucleic acid that contains genetic information. 6. RNA : RNA is a single-stranded nucleic acid that contains genetic information in viruses and helps in protein synthesis in eukaryotes.7. Chromosomes : The thread-like microscopic structures made up of histone proteins and DNA and present in the nucleus of a cell are called chromosomes.8. Chromatids : The two identical thread-like strands of a longitudinally split chromosome are called chromatids.9. Centromere : The chromatids are connected together by a central spherical body called centromere.10. Autosomes : The chromosomes which contain genetic information for physical characteristics of our body except the sex are called autosomes. They are also called somatic chromosomes. 11. Sex chromosomes : The chromosomes which contain genetic information for determining the sex of the foetus are called sex chromosomes. They are also called heterosomes.12. Gametes : The haploid reproductive cells produced from gonads are called gametes. 13. Sex determination : The process in which the sex of the foetus is determined by the sex chromosomes present in the gametes is called sex determination.14. Crossing over: The exchange of genetic materials during meiosis I is called crossing over. 15. Gametogenesis: The formation of gametes in gonads is called gametogenesis.Sequence of Curriculum Issued by CDC Concept of mitosis and meiosis cell division Importance of mitosis and meiosis cell division Differences between mitosis and meiosis cell division (based on number of daughter cells, number of chromosomes and types of dividing cells) Chromosomes, DNA and RNA (introduction and differences) Role of sex chromosomes in sex determination of human beingsUNITCell Division and Sex Determination 4.1Estimated teaching period Theory Practical4 1Bodhraj Acharya, born on April 21, 1977, in Chitwan, Nepal, is a Nepalese-born American professional who has made substantial strides in laboratory medicine, cell biology, and chemistry. With a wealth of experience as a clinical laboratory technical director and as a Clinical Laboratory expert for non-profit organizations, Acharya has played a pivotal role in enhancing medical diagnostics and research. Bodhraj AcharyaAbout the Nepalese Scientist

64 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 65The CellObserve a building. What raw materials are used to make it? At the same time observe the wall of the building. What are used to make it? Obviously, the wall of a building is made up of many bricks. These bricks are the basic units to make the structure of the whole building. Similarly, a multicellular organism is made up of many cells. The body of living beings is made up of microscopic components called cells. Thus, the fundamental, structural, and functional unit of life is called the cell. Protoplasm, cell organelles and inclusions are the building blocks of cells. A cell is self-contained and performs vital biological activities.Ribosomecytoplasmmicrotubulescentriolesnucleusnucleolusgolgi apparatusmitochondrioncell membraneSmooth eRendoplasmicreticulum (eR)lysosomecell wall Pinocytotic vesiclecell membranegolgi apparatuschloroplastvacuole membraneRaphide crystaldruse crystalmitochondriacytoplasmlarge central vacuoleRough (eR)nucleusnucleolusendoplasmic reticulum (eR)RibosomeFigure: a plant cell and an animal cellCell DivisionEvery organism begins as a single cell. New cells are regularly formed from pre-existing ones. Cell division is the biological process through which a pre-existing diploid cell divides into two or four daughter cells. It is a significant phenomenon that occurs in all living things. Cell division is the process by which new cells are formed.The cell division occurs in three distinct phases. They are interphase, M phase and cytokinesis. The cells get ready for cell division during interphase. The M phase is the stage in which karyokinesis takes place. The division of one nucleus into two or four nuclei is called karyokinesis. The nucleus divides into two during mitosis and divides into four during meiosis. After the nuclear division, cytokinesis takes place. Cytokinesis is the process in which the cytoplasm of the cell divides. During mitosis, the cytoplasm divides into two parts. During meiosis, the cytoplasm divides into four parts.Figure: a cell divides into two daughter cells

64 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 65Importance of cell divisionCell division is a very important characteristic of living things. Cell division helps in physical growth and development, healing, repair, formation of new blood cells and formation of gamete. The unicellular organisms usually reproduce by cell division. It could be amitosis, binary fission or multiple fission. Multicellular organisms grow in shape and size by mitosis cell division. It helps in healing of wounds. New cells arise from the old ones in the cuts and wounds and recover the damage. New blood cells arise from cell division. Sexual reproduction is only possible because the mitosis cell division helps to produce haploid gametes. Types of cell divisionThe cell division is broadly divided into two types. They are mitosis and meiosis. It is based on the number of chromosomes in daughter cells compared to the mother cell. Mitosis (Somatic Cell Division)In 1877 AD, German biologist Walter Flemming, for the first time observed the phenomenon of the mitosis or mitotic cell division. Mitosis produces two daughter cells that are identical to the mother cell in every aspect. As a result, it is also known as equational cell division. Thus, mitosis is an equational division in which a mother cell divides into two identical daughter cells. Mitotic cell division keeps the same (i.e. diploid) number of chromosomes as the parent cell in each division of the cell. Mitosis is the biological division of a diploid parent cell into two diploid daughter cells. Mitosis occurs in either vegetative or somatic cells. As a result, it is also known as somatic cell division. It is mainly responsible for growth and development of an organism.Figure: a mitosis cell divisionFeatures of mitosisi. The daughter cell is also diploid. It has two sets of chromosomes. One set from the father and another set from the mother.ii. One mother cell divides into two daughter cells.iii. The number of chromosomes in the mother cell equals to number of chromosomes in the daughter cell. Therefore it is also called equational cell division.iv. Daughter cells are identical to mother cells because there is no crossing over. No genetic materials are exchanged.v. It does not help much in evolution.

66 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 67Significance of mitosisMajor significances of mitosis cell division are it helps in the healing of wounds, physical growth and development, repair of the body and production of blood cells.i. Mitotic cell division is very important in the growth and development of the body because the mitotic cell division produces new somatic diploid cells for the growth of the body, tissue repair and healing of wounds. ii. It also produces new blood cells to replace the dead blood corpuscles. iii. Mitosis produces new cells to replace old dying cells. Without mitosis, the body would not grow and injuries would not heal.iv. The mitosis cell division helps in the asexual reproduction of unicellular organisms. For example, some bacteria and amoeba reproduce asexually with the help of mitosis cell division. A diploid mother organism will split into two diploid daughter organisms. v. Mitosis helps to maintain genetic stability. Meiosis (Gametic Cell Division)Meiosis cell division is another type of cell division. It does not occur in other parts of the body. It occurs in the germ cells of reproductive parts of the body. For example, it occurs in male gonads and female gonads in human beings. It occurs in the anther of the stamen and ovary of the carpel of flowers. Meiosis cell division is the process in which one diploid mother cell divides into four haploid daughter cells. First of all, the germ cells get ready for cell division. Then the M-phase will start. It occurs in two stages, Meiosis I and Meiosis II. During ‘meiosis I’ karyokinesis will occur. The identical chromosomes also called homologous chromosomes pair up. They stay connected at chiasmata. They can exchange genetic materials through chiasmata. The genes will reshuffle and slightly varied genes will be formed. Due to this variation occurs in the daughter cells. Then meiosis II starts. During meiosis II the four nuclei are formed. Now, the cytokinesis will start and the cytoplasm will divide into four daughter cells. Figure: a meiosis cell divisionDaughter cells have slightly different genetic makeup compared to mother cells. MEMORY TIPS

66 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 67Meiosis cell division is called reduction cell division because the number of chromosomes is reduced to half in the daughter cell compared to the mother cells. Meiosis cell division brings variation because genetic materials are exchanged during crossing over in the first karyokinesis of meiosis cell division. Variation is a distinct difference seen between two individuals. Meiosis cell division is responsible for the formation of gametes, sexual reproduction and evolution.Features of meiosis cell divisioni. The main features of meiosis are it occurs in germ cells, produces haploid reproductive cells and helps in sexual reproduction. ii. If a mother cell is diploid, the daughter cell will be haploid regarding the number of chromosomes after a meiosis cell division.iii. In meiosis cell division four cells are formed in second cytokinesis. iv. The daughter cells will be slightly different from the mother cells. v. It helps in evolution. vi. Meiosis produces reproductive cells. Meiosis occurs in germ cells only. Significance of meiosis cell division The significance of meiosis cell division is it helps in the formation of gametes in animals and the formation of pollen grains in plants for sexual reproduction. It helps to bring variation and evolution.i. Meiosis is very important in sexual reproduction because meiosis makes gametes. The meiosis in the germ cells of the male gonads makes the male gamete. Meiosis in the anther makes pollen grains. Meiosis in the female gonads makes female gametes. In plants meiosis in ovule makes ovum. ii. Meiosis cell division produces a haploid set of chromosomes in daughter cells. Then after the fusion of male gamete and female gamete, a zygote can again have diploid chromosomes. It helps to maintain genetic stability.iii. It helps to repair defective genes, avoid genetic disease and repair genetic disorders.iv. Crossing over occurs in meiosis. So, daughter cells are slightly different from the mother cells. So, it helps in evolution. Differences between mitosis and meiosisS.N. Mitosis S.N. Meiosis1. It is the division of a diploid mother cell into two diploid daughter cells.1. It is the division of a diploid mother cell into four haploid daughter cells.2. Mitosis cell division occurs in the somatic cells.2. Meiosis cell division occurs during gamete formation in reproductive cells.3. The daughter cells are identical to the mother cell in every aspect.3. The daughter cells differ from the mother cells as they have haploid chromosomes with variation of gene.No meiosis cell division in gonads makes a person infertile.MEMORY TIPS

68 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 69Introduction to chromosomeNo organism survives forever. All of them are mortal. This happens in the same way in case of their offsprings, too. Have you ever wondered why human babies resemble humans? Why do they look like their parents? Offsprings of an organism look alike, and so it is in humans. This is possible because there are some structures inside our cells. These structures act like the blueprints of the human being, same as how an engineer knows the shape of the building before it is built using a blueprint map. The structures that carry this information of our bodies are hidden inside the nucleus of all eukaryotic cells. These structures are called chromosomes. In most eukaryotic cells, chromosomes are generally present more than two in numbers. The word chromosome is derived from the Greek words ‘khroma’ meaning colour and ‘soma’ meaning body. It is because when they were being researched, they looked colourful under microscope due to staining. Chromosomes are called the blueprint of an organism. Chromosomes are called blueprints of an organism because they contain DNA. DNA contains genes. Genes have codes to make our physical bodies and habits. FACTS WITH REASONNucleic acid Nucleic acids are the acids that are found in the cells. The nucleic acid is made of nitrogen base, sugar and phosphoric acid. It contains hereditary information, stores genes and also helps in protein synthesis. It is broadly divided into two types. They are deoxyribonucleic acid and ribonucleic acid. Deoxyribonucleic acid (DNA)DNA is a double-stranded nucleic acid found in chromosomes which contains hereditary information. DNA stands for deoxyribonucleic acid. LocationDNA is present in most living organisms. DNA is found floating in the cytoplasm of prokaryotic organisms. The bacteria do not have a developed nucleus. So, the DNA acts as a nucleic core and stores the hereditary information of bacteria. The DNA virus also has DNA as its nucleic core. DNA is present inside the capsid. Every eukaryotic organism contains DNA. The DNA is found in the chromosomes in the nucleus of the cell. The segments of DNA are called genes. StructureDNA is made of Nitrogen bases, deoxyribose sugar and phosphoric acid. The combination of a nitrogen base and CellNucleusChromosomeChromosomeIf the person is exposed to highintensity radiation for long, it could destroy the DNA of the cell.Memory Tips

68 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 69sugar (deoxyribose sugar) makes a nucleoside. If a phosphate ion attaches to a nucleoside, it makes a nucleotide. Nucleotide is a combination of a nitrogen base, deoxyribose sugar and a phosphate ion. Nucleotides are monomers. Many nucleotides combine to make a polymer of nucleotide, which is a DNA. DNA is a polynucleotide which has two antiparallel strands. The nucleotide is different from person to person. So, its quality varies from person to person. Nitrogen bases found in DNA are (ATGC) adenine, guanine, cytosine and thymine. Adenine is paired with thymine with a double bond. Guanine is bonded with cytosine with a triple bond. Functions of DNAThe general functions of DNA are it stores hereditary information, transfers hereditary information from the mother cell to the daughter cell and forms RNA by transcription. i. DNA (deoxyribonucleic acid) is a genetic material that is responsible for the transmission of genetic information from one generation to the next. ii. DNA can help in the formation of RNA by the process of transcription. It helps to make protein.iii. The role of DNA in prokaryotic cells is to work as a nucleus to store genetic information, control the activities of cells etc. iv. The function of DNA is to code for proteins and store hereditary information. v. DNA determines our physical appearance, IQ, heredity, habits and other things. Ribonucleic acid (RNA)RNA is a single-stranded nucleic acid that contains genetic information in viruses and helps in protein synthesis in eukaryotes. RNA stands for ribonucleic acid. LocationRNA is found in the cytoplasm of the organisms. RNA is also present in RNA viruses. It is present inside the capsid. Some of them are found in chromosomes also. StructureRNA is also a polynucleotide. It means it is also made of nucleotides. RNA has a single strand. It is made of a combination of nitrogen base, ribose sugar and phosphate ion. The nitrogen base and sugar (ribose sugar) make nucleosides. It combines with phosphate ions to make nucleotides. Many nucleotides join together to form polynucleotides. It contains four nitrogen bases. They are Figure: Structure of DNARNA and DNA are polymers made of monomers called nucleotides. MEMORY TIPSFigure: Structure of RNAIf the DNA transcription fails, RNA will not be made. MEMORY TIPS

70 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 71(AUGC) adenine, uracil, guanine and cytosine. Adenine pairs with uracil with double bonds. Guanine pairs with cytosine with triple bonds. Function:i. RNA is mainly responsible for protein synthesis. ii. RNA stores hereditary information in RNA viruses.iii. It transfers hereditary information from one generation to another generation of the virus. Types of RNAThe three types of RNA are Messenger RNA, ribosomal RNA and transfer RNA.The functions of RNA are:i. Messenger RNA (mRNA): takes messages from DNA to make proteinii. Ribosomal RNA (rRNA): makes major part of RNAiii. Transfer RNA: transfers amino acid to make protein Differences between DNA and RNADNA RNA1. DNA contain two anti-parallel strands. 1. RNA contain single strand.2. DNA is mainly responsible for heredity. 2. RNA is mainly responsible for protein synthesis. 3. It contains deoxyribose sugar. 3. It contains ribose sugar.4. It is found in the chromosomes in the nucleus.4. It is found in the cytoplasm mostly and sometimes in chromosomes too.5. It can do transcription. 5. It is formed by DNA by transcription.Structure of a chromosomeWhen we observe a nucleus of a cell, we see fine elongated thread-like structures called chromatin fibres or chromatin network. Chromatin fibres are made up of DNA, proteins and minerals. During cell division, these chromatin fibres become shorter, thicker and condensed. The thread-like microscopic structures made up of histon proteins and DNA and present in the nucleus of a cell are called chromosomes. A chromosome is made up of mainly two parts. They are chromatid and centromere.a) ChromatidsAn undivided chromosome (before cell division) has one chromatid containing a single molecule of DNA. During cell division, the chromosomes divide and form an exact copy of each chromatid by a process called DNA replication. Thus, after division, there will be exact two copies of DNA molecules. The two identical thread-like strands of a replicated chromosome are called chromatids. These two newly formed chromatids from a single chromosome are also called sister chromatids. A chromosome usually has two arms. They are p-arm and q-arm. The length of p-arm and q-arm may or may not Chromosome is made up of DNA and histon protein.MEMORY TIPSp-armq-armChromatids TelomereCentromereChromatids

70 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 71be equal. There is a specific protein at the end of all chromosomes called telomere that prevents the fusion of chromosomes among each other. b) Centromere or primary constriction or kinetochoreThe chromatids are connected together by a central spherical body called centromere. Centromere attaches the arms of the chromatids together. Since centromere is the body which helps in the movement of chromosomes towards the opposite poles of the cells, it is also called kinetochore. During cell division, the chromatids attach to the thread-like structures called spindle fibres and help in dividing the chromosomes. Some couples have either male-only or female-only kids. Though males have both X and Y sex chromosomes, some couples have either male-only or female-only kids because of unpredictable heredity and coincidence. FACTS WITH REASONNumber of chromosomesThe total number of chromosomes present in the nucleus of the cell is fixed for each organism. The cell which has two sets of chromosomes is called diploid. One set came from the father and another set came from the mother. Somatic cells, zygotes etc are diploid cells. The cell which has one set of chromosomes is called a haploid cell. Gametes, pollen grains etc are haploid cells. A somatic cell of a human being has 23 pairs of chromosomes. 23 came from the father and 23 came from the mother. Gametes of humans are haploids. Sperms have 23 chromosomes and ovum has 23 chromosomes. Among 23 pairs of chromosomes, 22 pairs are somatic chromosomes and 1 pair is sex chromosomes in a human being. The gorilla has 24 pairs (48) chromosomes. The female bee has 32 chromosomes. The male bee has 16 chromosomes. So, drone bees are haploid. Types of chromosomesThere are 46 chromosomes in a human cell. They stay in pairs. So, there are 23 pairs of chromosomes in a human cell. Each of them is unique and has different functions. However, these chromosomes are broadly divided into two groups. They are somatic chromosomes and sex chromosomes. They are classified based on their functions. Somatic chromosomesThe somatic chromosomes contain codes for physical properties of the body other than the sex. They determine the height, complexion, habit, heredity and many other characteristics of the body but they cannot determine the sex of the foetus. The chromosomes that are responsible for the physical characteristics of the body other than the sex of the foetus are called somatic chromosomes. Both chromosomes of the pair of somatic chromosomes are identical to each other. They contain similar genetic codes. So, they are called autosomes. There are 22 pairs of Y chromosome is shorter than X chromosome.MEMORY TIPSThe karyotype for human males is 44 + XY and for the human females is 44 + XX. MEMORY TIPS

72 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 73somatic chromosomes in a human cell. The somatic chromosomes of males and females are similar. Sex chromosomesThe sex chromosomes contain codes for the sex determination of the foetus. They determine the sex of the child. They do not determine other physical characteristics of the body. The chromosomes that are responsible for the sex determination of the foetus are called sex chromosomes. The chromosomes of the pair of the sex chromosomes are different from each other. They contain different genetic codes. So, they are called heterosomes. There is one pair of sex chromosomes in a human cell. The sex chromosomes of males and females are different. Male sex chromosomes are usually represented as XY. The symbols X and Y are trying to imply that the two sex chromosomes present in the male are different from each other. The female sex chromosomes are represented as XX. The symbol is trying to clarify that both of the female sex chromosomes are similar to each other and also similar to the first sex chromosome of the male. Human chromosomesGamete formationGametes are reproductive cells. They contain one set of chromosomes. They are called haploid cells. They are produced by meiosis cell division in germ cells in reproductive organs. In a human being, the male gametes are produced by the male gonads called testicles and the female gametes are produced by female gonads called ovaries. If the meiotic cell division does not occur in the germ cell of the gonad of an organism, then the organism will be infertile. The male sex chromosome has XY chromosomes. When the male gamete called sperm is formed, each male gamete gets either X or Y chromosome. So, 50% of male gamete must have an ‘X’ chromosome. Its karyotype will be 22 + X. Another 50% of gamete must have a The damage in DNA while making copies of DNA during meiosis can cause genetic disorders in the foetus.MEMORY TIPS

72 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 73‘Y’ chromosome. Its karyotype will be 22 + Y. There is no chance that 100% of male gamete contain X chromosomes only or Y chromosomes only. The female sex chromosomes have XX chromosomes. When the female gametes called egg or ovum is formed, each female gamete gets X chromosomes only. Its karyotype will be 22 + X. 100 % of female gametes contain X chromosomes. Therefore, they do not have a role in the determination of the sex of the child. Sex determination The biological cause for an organism developing into one sex or the other due to the genes in the fused gametes is called sex determination. The sex of an offspring is determined by a pair of chromosomes called sex chromosomes. These sex chromosomes are present in all cells including the sperms and egg. In female, the egg cells have identical sex chromosomes. They are represented by X and X. But, in males, they have different sex chromosomes. They are represented as X and Y. If the sperm having an X- chromosome meets with an egg having X-chromosome, a baby girl is born. Likewise, if a sperm having Y-chromosome meets with an egg having X-chromosome, a baby boy is born. The chart to explain sex determination is given below.From the given information, it is clear that a female has same sets of chromosomes in her egg cells (22+X) but a male has two different types of chromosomes in his sperm cells (22+X and 22+Y). Therefore, the sex determination fully depends upon the type of male sperm (X or Y) which fuses with the egg (both X). Hence, the female has no role in sex determination. Parents →Result in F1-generationFather MotherSperm Sperm OvumOvum (female)Sperms (male)Girl (daughter)Girl (daughter)Boy (son)Boy (son)OvumGametes →44+XY44+XX 44+XY44+XX44+XX 44+XY22+X22+X22+X22+X22+X 22+Y22+Y 22+XThe two similar sex chromosomes in a female cell are called homogametic chromosomes. Likewise, the two different sex chromosomes in a male are called heterogametic chromosomes. Males generally have heterogametic chromosomes and females generally have homogametic chromosomes.MEMORY TIPS

74 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 75The probability of a child being either a boy or a girl is ½. The probability of a child being either a boy or a girl is ½ or 50% because half of sperms contain X chromosomes and another half of sperms contain Y chromosomes. All of the female gametes contain X chromosomes, so they do not change the probability of a child being either a boy or a girl. FACTS WITH REASONHOT SKILL HIGHER ORDER THINKING SKILL1. A little child grows into a teen and then into an adult. Mention the type of cell division which is responsible for the growth and development of the body.A little child grows into a teen and then into an adult. The cell division responsible for such growth and development of the body is mitosis cell division. 2. Chromosomes are called vehicles of heredity. Chromosomes are called vehicles of heredity because it contains DNA that contains our hereditary information. It is transferred to children from parents. 3. Animals and plants have definite characteristics. Animals and plants have a definite number of chromosomes. Each chromosome has a definite number of genes. Each gene carries one character from one generation to another. So, animals and plants have definite characteristics. 4. What is the role of DNA in prokaryotic cells?The role of DNA in prokaryotic cells is to work as a nucleus to store genetic information, control the activities of cells etc. 5. Somatic chromosomes are called autosomes. Somatic chromosomes are called autosomes because both chromosomes of the allele are similar.6. Explain the importance of mitotic cell division in the growth and development of the body.Mitotic cell division is very important in the growth and development of the body because the mitotic cell division produces new somatic diploid cells for the growth of the body, tissue repair and healing of wounds. It also produces new blood cells to continue circulation. Mitosis produces new cells to replace old dying cells. Without mitosis, the body would not grow and injuries would not heal.7. Sexual reproduction is impossible without meiotic cell division.Sexual reproduction is impossible without meiotic cell division because we need male gamete and female gamete for sexual reproduction. Gametes are produced by sexual reproduction only. 8. A couple has four girls. Now, what will be the probability of the gender of the next baby.The probability of new born child being either a girl or a boy is 50-50. This is because there is an equal chance of the fusion of sperm having an X-chromosome and a Y-chromosome with the egg of a female having an X-chromosome. 9. Differentiate between autosomes and sex chromosomes.The differences between autosomes and sex chromosomes are:

74 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 75S.N. Autosomes S.N. Sex chromosomes1. Autosomes determine somatic body structure.1. Sex chromosomes determine the gender of the offspring.2. There are 22 pairs of autosomes in the cells of the human body.2. There is one pair of sex chromosomes in the cells of the human body.10. Identify the girl and boy in A and B. Mother →Father ↓22+X 22+X22+X A 44+XX22+Y 44+XY BA has 44+XX chromosomes. So, it is a girl. Similarly B has 44+XY chromosomes. So, it is a boy.4 STEPS EXERCISE EXERCISESTEP11. Multiple choice questions a. Where are the chromosomes located?i. ribosome ii. genes iii. DNA iv. nucleoplasm b. How do the characteristics of parents transfer to the children?i. through the blood ii. through the food iii. through the genes iv. through the environment c. The fertilization in humans is shown in the concept map below. Write the karyotype of B.A X fuse with Ovum Y B fuse withi. male ii. Female iii. 44 + XX iv. 44 + XY d. Which one is a meiosis cell division?Exchange of genetic materials No exchange of genetic materials Variation in daughter cells A BIdentical daughter cells C D i. A ii. Biii. C iv. De. How does cell division occur in the living being?i. cells get ready for division → karyokinesis → cytokinesis → daughter cells

76 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 77ii. karyokinesis → interphase → cytokinesis → daughter cells iii. M-phase → interphase → daughter cells → cytokinesis iv. mitosis → karyokinesis → meiosis → cytokinesis f. What are the steps of meiosis?i. meiosis I → interphase → karyokinesis → cytokinesis → meiosis II →karyokinesis → cytokinesis ii. mitosis → karyokinesis → meiosis → cytokinesisiii. cells get ready for division→karyokinesis→cytokinesis→meiosis I iv. M-phase → interphase → daughter cells → cytokinesis g. What defines the gene?i. segment of DNA, stores hereditary information, can pass from parents to offspringii. makes chromosomes, can mutate, releases energy in the cell iii. contains hereditary information, polynucleotide, double-stranded iv. polynucleotide, protein synthesis, single-stranded h. Sex chromosomes are called heterosomes. Why? i. They are transferred automatically to offspring.ii. Both chromosomes of the allele are genetically similar to each other.iii. Two chromosomes of the allele are different from each other.iv. There are 22 pairs of somatic chromosomes. i. Study the given dialogue between three people in a tea shop and decide who is right or wrong. Hari: Sad as it is but you must marry another wife. Rama is not able to give birth to any daughters. Krishna: I agree ! You already have three sons. You should marry another one.Ram: No! It's not her fault for giving birth to sons only. First of all, she has no role in the sex determination of a child because she does not have Y chromosomes. i. Hari and Krishna are right but Ram is wrong. ii. Hari is wrong but Krishna and Ram are correct. iii. Ram is right but Hari and Krishna are wrong. iv. Hari is right. Krishna and Ram are wrong. j. Which of the following are haploid cells? i. pollengrains, spores, ovum, zygoteii. eggs, sperm, antherozoids, embryo iii. ovum, pollen grains, germ cells, neuron iv. egg, male gamete, pollen grains, haploid spores a. iv b. iii c. iv d. i e. i f. i g. i h. iii i. iii j. ivAns of MCQSTEP22. Very short questionsa. Zygote is unicellular. Which cell division changes it into the multicellular structure?b. What type of cell division is A?

76 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 77CellsABCell divisionSomatic cells Reproductive cells daughter cells c. If 50 % male gamete of humans contains X chromosomes, how many percentages of the female gamete of humans contains X chromosomes? d. Write the function of B in an eukaryote. A BNitrogen base ATGC AUGCLocation Nucleoplasm Cytoplasm e. If a mother cell is diploid, what will be the daughter cells regarding the number of chromosomes after mitosis cell division? f. Which one is male? g. Write the full form of RNA and DNA. h. If meiosis cell division does not work in gonads, what problems does a person suffer from?i. A couple has three girls. Now, what will be the probability of the gender of the fourth baby to be born? STEP33. Short questions a. Even though offspring from the same parents share some similarities, they cannot be identical. Give reason. b. Differentiate between mitosis and meiosis. c. Write any two advantages of the type of cell division A. Types of cell division Crossing over Daughter cells A Yes Haploid B No Diploid

78 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 79d. Draw the diagram of the chromosome and label the centromere. e. Write the pairs of nitrogen bases found in DNA and the number of bonds between them.f. Write the characteristics of the mitosis cell division. g. Let’s say a man and woman got married and produced a child. How does cell division help them in this process? h. What are the sugar and bases present in the structure given below?STEP44. Long questions a. Rammaya has given birth to three daughters only. Her family is blaming her for giving birth to daughters. With the help of a sex-determination chart, justify that Rammaya is not responsible for the birth of daughters.b. Describe the structure of the DNA along with its suitable diagram.c. What is cell division? How does it happen? Describe in short. d. What is mitosis cell division? Compare it with meiosis cell division.e. Study the given concept map and answer the following questions. CellsABCell divisionchromosomes of allele are similar chromosomes of allele are different Write the name of A and B. Mention the function of B.Project WorkWith the help of colourful threads make the different types of chromosomes and display in your class.♦♦♦

78 cell diviSion and Sex deteRmination Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 79Key terms and terminologies of the unit1. Heredity : The process by which parental characteristics are transferred to their offspring is known as heredity or inheritance. 2. Gene : A gene is a segment of DNA which is responsible to transfer parental characters from one generation to the next generation.3. Allele : An alternative form of matching genes is called allele.4. Dominant character : The character that expresses itself by suppressing the other character is called the dominant character.5. Recessive character : The character which fails to get expressed in the first generation and usually hides itself is known as the recessive character.6. Monohybrid cross : The cross involving one pair of contrasting characteristics is called monohybrid cross. 7. Dihybrid cross : The cross involving two pairs of contrasting characteristics is called dihybrid cross.8. Genetics : The branch of biology that deals with genes, heredity and variation in the organisms is known as genetics.9. Phenotype : Phenotype is the characteristic that is seen in an organism from outside.10. Genotype : The genetic make-up of an organism is called genotype.11. Law of dominance : In the crossing between the pure parents having a pair of contrasting characters, only one character appears in the F1 generation as a dominant character while other character remains hidden as a recessive character. 12. Law of Segregation : The dominant and recessive characters of the hybrids separate during the gamete formation in such a way that each gamete receives only one character at a time.13. Variation : The difference in genotype and phenotype of the organisms in each successive generation is known as variation. Sequence of Curriculum Issued by CDC Introduction to gene Reason to select pea plant in Mendel experiment Dominant and recessive characters: introduction and examples Mendel’s law: related to monohybrid cross onlyUNITHeredity and Mendelism4.2Estimated teaching periods Theory Practical5 1Dayananda Bajracharya, born on September 22, 1945, in Kathmandu, Nepal, was a revered figure in Nepalese biology and science communication. His impactful contributions to our comprehension of Nepal's biodiversity through seminal works like \"Wildlife of Nepal\" and \"Ichthyology of Nepal\" remain unmatched. Dayananda BajracharyaAbout the Nepalese Scientist

80 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 8114. Hereditary variation : The type of variation which is caused due to the usual changes in the genes of the parental gametes is called hereditary variation.15. Environmental variation: The variation in the phenotype of the organisms which occurs due to environmental factors like climate, nutrition, lifestyle, culture, etc. is known as environmental variation.16. Continuous variation : The variation that occurs in the following generations in variety of possible limits is known as continuous variation. 17. Discontinuous variation : The variation that occurs within a limited range of options is known as the discontinuous variation.18. Mutation : Mutation is the sudden permanent change in the DNA or genes that alters the genotype or phenotype of an organism.IntroductionLiving organisms have a tendency to produce offspring of the same kind. As a result, continuity of the generation takes place. In each successive generation, more or less parental characteristics such as physical appearance, nature, behaviour, etc. transfer to their offspring. This transfer takes place either through the somatic cells (as in asexual reproduction) or through gametes (as in sexual reproduction). In both sexual and asexual reproduction, the parental characteristics are transferred to their children with the help of genes which are present in the nucleus of the cell. Thus,the process by which parental characteristics are transferred to their offspring is known as heredity or inheritance. Some characteristics like appearance, structure, certain body abilities (like little finger twisting, hitchhiker’s thumb etc.) are transferred to the offspring are called hereditary characteristics. But, some characters that are gained by the people in their lifetime like education, skill, knowledge, body building, etc. not transferred to the offspring are called acquired characteristics.Genes and InheritanceThe nucleus of every eukaryotic cell contains long, thin and coiled structures called chromosomes. Humans have 23 pairs of chromosomes. Chromosomes are made up of DNA molecules and histone protein. There are specific segments of DNA which act as a single unit to carry the parental characters from one generation to the next generation that are called genes. Genes can store a variety of characters like hair colour, colour of skin, height, personality, etc. There are about 20,000 known genes in the human chromosomes. Genes help to produce specific proteins that can perform a certain function in the body. GrandparentsGeneration 1 Generation 2HeredityThe characteristics that can be transferred from parents to the offspring are called hereditary characteristics. MEMORY TIPSA gene is a segment of DNA which is responsible to transfer parental character from one generation to the next generation.MEMORY TIPS

80 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 81Functions of genesi. Genes store hereditary information.ii. Genes transfer hereditary information from parents to offspring. iii. Genes contain codes for protein synthesis. iv. Genes can reshuffle during sexual reproduction to bring variation.v. Mutation in genes and genetic recombination can cause evolution. Some terminologies useful in this unita) Alleles or allelomorphsAll 46 chromosomes in the cell of a human body are in pair. In a pair, one chromosome comes from father and another comes from mother. In each pair, the chromosomes are identical in shape, nature and size. The genes present in them are on the same position. Consider the gene for height. There can be two variants for height gene, i.e. dwarf and tall. These variants are called alleles or allelomorphs. That is, each of two alternative forms of a gene on the chromosomes of an individual's cell are called alleles. So, we have two alleles for height, i.e. tall allele and dwarf allele. The allele in the chromosomes can be similar (tall-tall or dwarf-dwarf) or different (tall-dwarf). Similarly, other organisms also have such alleles in their chromosomes.b) Dominant and recessive alleleOut of the two alleles, one allele has the tendency to suppress the other allele and appears in the first generation. The allele that expresses itself by suppressing the other allele is called the dominant allele. Similarly, the allele which fails to get expressed in the first generation and usually hides itself is known as the recessive allele. The tall allele is the dominant allele and the dwarf allele is recessive. The dominant allele is represented by a capital letter and the recessive allele is represented by a small letter. Example: “T” for tall and “t” for dwarf.c) Phenotype and GenotypePhenotype is the characteristic that is seen in an organism from outside. It is represented by words. Examples: tall, dwarf, red flower, green pod, black hair, free earlobe, etc.The genetic make-up of an organism is called genotype. Examples:i. TT – pure tall, both tall alleles from parents.ii. Tt - hybrid tall, tall allele from one parent and dwarf from other parentiii. tt – pure dwarf, both dwarf alleles from parentsAn alternative form of matching genes is called allele. Examples, TT, Tt, RR, Rr, etc.MEMORY TIPSAllelesViolet flowerWhite flowervvVVGenotypeWhat the gene itself look like What the gene doesPhenotypeGenotype and phenotype

82 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 83d) Homozygous and heterozygous allelesIf the genotype contains similar alleles, it is called homozygous or pure alleles. For example, TT and tt. If the genotype contains different alleles for a gene, it is called heterozygous or hybrid alleles. For example, Tt. e) Parental and filial generationsUsually during monohybrid cross the pure organisms of opposite contrasting characteristics are considered parental generation. The offspring produced by the crossing between two pure organisms of parental generation is usually called the first filial generation or F1 generation. Mostly they are all hybrid organisms. Only the dominant characteristics are seen in them. The offspring produced by the cross between individuals of the first filial generation are called the second filial generation or F2 generation. They can be pure dominant (25%), hybrid (50%) and pure recessive (25%). All types of phenotypes are visible in the F2 generation. f) Monohybrid cross and dihybrid crossThe cross involving one pair of contrasting characteristics is called monohybrid cross. Similarly, the cross involving two pairs of contrasting characteristics is called dihybrid cross. FACTS WITH REASONAll characters are seen in the F2 generation because of the law of purity of gamete. Dominant characteristics will be expressed in the F1 generation. The recessive characteristics are not lost during the cross at first filial generation. They remain hidden but pure. Recessive characteristics also go independently and separately into the gamete. As a result, there is a 25% chance that pure recessive characteristics will appear, a 25% chance that pure dominant characteristics will appear and a 50% chance that hybrid organisms will appear. Genetics and MendelismThe branch of biology that deals with heredity and variation in the organisms is known as genetics. There are various sub-branches in genetics like behavioural genetics, developmental genetics, genetic engineering, medical genetics, etc. The history of genetics started in between 1856-1863 during which research was conducted for the first time on variation and genetics by an Austrian Monk called Gregor Johann Mendel. Mendel was born on July 22, 1822 AD. He joined a monastery and began researching on pea plants. After a long time experiment, Mendel proposed several laws. But, the significance of his work was unknown to everyone including himself. Mendel’s result was recognized only when such similar results were obtained by Carl Correns (Germany), Hugo De Vries (Holland) and Erich Von Tsermark (Austria). Mendel was then given credit to his theory of genetics. Therefore, he is known as the father of genetics. Mendel’s version of genetics is known as Mendelian genetics or Mendelism or Mendel’s theory of inheritance.FACTS WITH REASONGenes determine our physical traits. Genes determine our physical traits because they contain hereditary information and codes for our physical appearance and habits. They brought this hereditary information and codes from our parents. So, our physical traits will match our parents.

82 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 83Mendel’s material for his experimentMendel wanted to study how characteristics are transferred from parents to offspring. So, he chose the common pea plant (Pisum sativum) for his experiment. He conducted several experiments in the Monastery garden at Brunn, Austria. The reasons for choosing pea plant for his experiment are:i. Pea plant has a short life span and produces multiple fertile offspring due to which study can be done easily.ii. They are easy to cultivate as they grow well in gardens.iii. The flowers of the pea plant are bisexual. So, both self and cross-pollination are possible.iv. In a pea plant, there are many pairs of distinct contrasting characteristics.v. Pea plants have average size and are easy to handle.vi. The hybrids obtained by crossing the pea seeds are also fertile. Recessive traitDominanttraitHeight Seed shape Seed colour Seed coat Pod shape Pod colour Flower positionDwarf Wrinkled Green White Constricted (flat)Yellow TerminalTall Round Yellow Green Inflated (full) Green AxialMendel's material for his experiment with its traitsMendel chose seven pairs of contrasting characteristics in pea plants. They are given in the table:S.N. Characteristics Contrasting pairsDominant Recessive1 Shape of seeds Round Wrinkle2. Height of the plant Tall Dwarf3. Colour of the flower Purple (Red) White4. Position of flower Axial Terminal5. Colour of pods Green Yellow6. Colour of seeds Yellow Green7. Shape of pods Inflated Constricted

84 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 85FACTS WITH REASONWhy did Mendel choose pea plant for his experiment?A pea plant has short life span. It is easy to cultivate. It produces fertile offspring. It is easy to do self-and cross-pollination in pea plant, it has many pairs of contrasting characters and they are easy to handle. So, Mendel chose pea plant for his experiment.The Method of ExperimentMendel carried out his experiment on the pea plants and noted the results very carefully. First of all, he had chosen single trait in the pea plants with their contrasting characters. For example, height (tall pea plant-TT and dwarf pea plant-tt). Then, he cross-fertilized these pea plants by cross-pollination. To avoid self-pollination in one of these flowers, he removed the male part (stamens) and made the flower unisexual. After the flower gave seeds, these seeds were shown.F1 generationThe pea plants that grew from these seeds represented the F1 or first filial generation. It was observed that all the plants of the F1 generation were tall. It is because the tall character in the pea plant is dominant over the dwarf one. These plants were called hybrid tall plants (Tt) as they contained the characteristics of both tall and the dwarf plants but they were phenotypically tall. After these plants were matured, their flowers were again allowed to self-pollination and then were fertilized. The seeds obtained from the plants of F1 generation were sown again. This represents F2 generation.F2 generationThe plants in F2 generation were surprisingly 75% tall and 25% dwarf. The ratio of tall and dwarf plants was 3:1 (3/4 tall and ¼ dwarf). Out of these four plants, one was pure tall (TT), two were hybrid tall (Tt) and the other was pure dwarf (tt).P generation F1 generation F2 generationTall Short Tall Tall Tall Tall Tall ShortMendel's experimentParents →Genotype →Pure tall pea plant Pure dwarf pea plantCross - pollinationF1 - generationF2 - generationF3 - generationGametesSelf-pollination →Possible gametes →All hybrid tall→Gametes →If the F1 - are bred togetherTtT tTTTtTTTtTtTTttttTTT Tt tt ttt T tTtttTT Tt

84 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 85Again, the plants in the F2 generation were self-pollinated and fertilized to obtain the result in F3 generation.Phenotype and genotype ratio in this experimentPhenotype is the characteristic that is seen in an organism from outside. Similarly, the genetic make-up of an organism is called genotype. In the second generation of pea plants obtained from Mendel's experiment, Phenotype ratio: 3:1(three tall and one dwarf)Genotype ratio: 1:2:1 (one pure tall, two hybrid tall and one pure dwarf).The conclusions of Mendel’s experiment i. The pure tall plants gave only tall offspring.ii. The pure dwarf plants produced only dwarf offspring.iii. The hybrid tall plants produced both tall and dwarf plants in the ratio of 3:1.Mendel tried this experiment with other pairs of contrasting characters and also found the same result. FACTS WITH REASONWhen Mendel crossed tall pea plants with dwarf pea plants and used those seeds to grow new plants, all of the new pea plants that germinated grew to be tall. When Mendel crossed tall pea plants with dwarf pea plants and used those seeds to grow new plants, all of the new pea plants that germinated grew to be tall because among pea plants being tall is a dominant characteristic. So, the genetic characteristic of being tall is expressed in the first filial generation. Being a dwarf is a recessive characteristic. So, it cannot be seen in the first filial generation. Mendel’s LawsMendel formulated three laws using the conclusions of his experiment. The three laws of Mendelism are given below.i. Mendel’s first law: The Law of Dominanceii. Mendel’s second law: The Law of Segregation or The Law of purity of gametesiii. Mendel’s third law: The Law of Independent Assortment(Note: Mendel's third law, i.e. law of independent assortment is not included in the syllabus of class 10.)Mendel’s first law: The Law of DominanceMendel’s law of dominance states that, “In the crossing between the pure parents having a pair of contrasting characters, only one character appears in the F1 generation as a dominant character while other character remains hidden as a recessive character.” Example of law of dominanceIn a cross between a pure tall pea plant (TT) and a pure dwarf pea plant (tt), the tall character appears as a dominant character over the dwarf character. So, all the plants in the F1 generation are tall.

86 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 87T T t tParents →Genotype →Pure tallGametesCross-pollinationOffspring inF1-generation Tall Tall Tall TallPure dwarfTt Tt Tt TtTT ttFACTS WITH REASONA recessive character is seen in the second filial generation.A recessive character is seen in the second filial generation because the genes of recessive characteristics did not blend in the first filial generation. It remained hidden and passed independently into the gamete and appeared in the second filial generation. This process is called the law of purity of gamete. Mendel’s second law: The Law of Segregation or The Law of purity of gametesMendel’s second law states that, “The dominant and recessive characters of the hybrids separate during the gamete formation in such a way that each gamete receives only one character at a time”.Consider a cross between pure tall and pure dwarf plants. In the F1 generation, all plants look phenotypically tall. Does it mean that the dwarf character has vanished from the gene? No ! It remains hidden as a recessive character in F1 generation. When gametes are formed by the plants of F1 generation, only one of them is expressed in the gametes. A single gamete cannot have both characters at a time. It means that in normal conditions, gametes can never be hybrid. As gametes contain only one character and are never hybrid, they are considered as pure. Hence, this law is also called as the law of purity of gametes.Example of law of segregationIn a cross between pure red flower of the pea plant (RR) and pure white flower of the pea plant (rr), all the flowers in F1 generation are red. There is no white flower in F1 generation. This is because red colour is a dominant character and white colour is a recessive character. If we allow self-pollination in the plants of F1 generation, we get two types of flowers in F2generation (75% red flower pea plants and 25% white flower pea plants). The result shows that phenotypic ratio is 3:1 and genotypic ratio is 1:2:1.A brown-skinned child can be born from white-skinned parents if both of those parents are hybrid white with recessive brown. MEMORY TIPS

86 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 87Parents - Pure redflowered pea plantPure white flowered pea plantRR rrRR Rr Rr rrR r R rRr Rr Rr RrR R r rGenotypesGametesCross-pollinationGametesPure redHybrid red Pure whiteF2 - generationSelf - pollinationF1 - generationGenetic characteristics in human beingsHumans have several dominant and recessive characters that are inherited from one generation to another. Some of the human characters are given below:S.N. Characteristics Contrasting pairsDominant Recessive1 Earlobes Free earlobes Attached earlobes2. Dimple Dimpled cheek Non-dimpled cheekCrossing in Some Organismsi) Fruit-fly (Drosophila melanogaster)A fruit fly is an insect. Some of them have very long wings and some of them have short wings. The longer wings are dominant characteristics. The shorter wings are recessive characteristics of fruit flies. When the fruit fly with a pure long wing was crossed with a pure short wing fruit fly, all of the new fruit flies produced in the first filial generation had long wings. This part of the experiment supported the law of dominance. Then again when two individuals of the first filial generation were crossed, some fruit flies had long wings and some fruit flies had short wings. 75 % of fruit flies had long wings and 25 % of fruit flies had short wings. This part of the experiment explained the law of purity of gamete. If a dihybrid cross is done, we can verify the law of independent assortment can also be verified. Hence the monohybrid cross of fruitflies supports Mendelism. Drosophila with short wingsDrosophila with long wingsDrosophila with long wings(Sibling crosses)Drosophila with long wingsDrosophila with long wingsDrosophila with long wingsDrosophila with short wings

88 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 89ii) Guinea pigA guinea pig is a mammal. It is a rodent similar to the mouse. It is also widely used for testing Mendalism. The contrasting character, the skin colour can be black or white. The black skin colour is dominant in the guinea pigs and the white skin colour is the recessive one. When the guinea pig with pure black skin was crossed with the guinea pig with pure white skin, all of the offspring in the first filial generation had black skin. It occurred according to the law of dominance. All offspring had black skin because the contrasting character black skin was dominant and expressed in the first filial generation. When two individuals from that first filial generation were crossed to produce the second filial generation, 75% offspring had black skin and 25% offspring had white skin. The phenotype was 3:1. Among the black ones, 25% were pure black and 50% were hybrid black. So, its genotype is 1:2:1. HOT SKILL HIGHER ORDER THINKING SKILL1. A white-skinned child was born to a dark-skinned parent. What is the reason for this?Since both parents are dark-skinned but gave birth to white-skinned, both of them must be hybrid black with recessive white characteristics. The recessive, white-skinned character has a 25% chance to reappear in the second filial generation. 2. Mendel's experiment can be done not only in plants but also in animals and humans. Mendel’s laws of genetics must work on any organism which has genes. So, it must also work on animals and humans because animals and humans also have genes. Let’s suppose there is an animal, that has chromosomes in its cells similar to the plants. The chromosomes are in pairs as an allele. The animals also have meiosis cell division to form gametes similar to plants. When crossed, animals also inherit traits from their parents. 3. Offspring obtained from the same parents show some similarities but they cannot exactly be similar to each other. Why? Write with reason. Children look like their parents because they inherit hereditary characteristics from their parents. But they are not exactly the same as parents because children receive some genes from the father and some from the mother. Some recessive characteristics may also appear.4. Mendel is called the 'Father of Genetics'. Mendel is called the father of genetics because he studied heredity and made three laws of genetics. 5. We cannot perform Mendel’s experiment on humans.Mendel’s experiment cannot be performed on human beings because of the following reasons:i. Human subjects are difficult to choose because they have to bear babies for the experiment.BBBB B B BB bb b b bbBBBb BbBbBbBbBbbbbb

88 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 89ii. It is unethical to obtain the offspring of F2 and F3 generations in human beings because fertilization has to be performed on brothers and sisters (same offspring of parents).iii. The country's law and human rights do not allow direct experiments on human beings. iv. The inheritance of the characters in human beings is much more complicated because one character is controlled by multiple genes. 6. State any three significances of Mendalism. What are the conclusions of Mendel’s experiment on pea plants? The significance of Mendalism is it propounded three laws of inheritance, explained the concept of inheritance and is the base for modern genetics. The conclusions of Mendel’s experiment on the pea plant are:There are some factors called genes that transfer characteristics from parent to child. Only the dominant characteristics are seen in the first filial generation (law of dominance). The contrasting characteristics do not blend, they can separate and go individually in each gamete (law of purity of gametes). The gametes can freely recombine in a dihybrid cross (law of independent assortment). 7. Mention the kind of puppies that are produced if a hybrid black dog breeds with a pure white dog. Show with a phylogenetic chart.Let the gamete of hybrid black dog be Bb.Let the gamete of pure white dog be bb.Monohybrid cross between a hybrid black dog and pure white dog be:Hybrid blackB b Purewhite b Bb bbb Bb bbWhen a hybrid black dog was crossed with a pure white dog following puppies can be produced.Phenotype = Black : White = 2:2Genotype = Hybrid black : Pure white = 2:2 Two puppies were black and two puppies were white. 8. List down the advantages of Mendelism.The advantages of Mendelism is:i. Using Mendelism, we can obtain disease-resistant and high-yielding varieties of plants and animals.ii. We can get a hybrid of the desired characteristics.iii. Dominant and recessive characteristics of the organisms can be identified.iv. We can predict the genotype and phenotype of the organisms by using Mendelism.9. Write down the percentage of tall and dwarf pea plants in F2 generation of a cross between pure parents with genotypes TT and tt.The percentage of tall pea plants is 75% and that of dwarf plants is 25%.

90 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 914 STEPS EXERCISE EXERCISESTEP11. Multiple Choice Questions a. When a pure tall pea plant and a pure dwarf pea plant are crossed, what will be the phenotype of offspring in the first filial generation?i. tall ii. pure tall iii. hybrid tall iv. dwarfb. What are the traits that transfer from parents to offspring called?i. contrasting characteristics ii. hereditary characteristics iii. recessive characteristics iv. dominant characteristicsc. Where are chromosomes located?i. cytoplasm ii. nucleoplasm iii. ribosome iv. centrosome d. Which of the following offspring is pure dominant? Contains recessive genes Does not contain a recessive gene Contains dominant genes A BDoes not contain dominant genes C D i. A ii. Biii. C iv. D e. In which order is Mendel’s experiment carried on?i. cross-pollination of pure organisms → first filial generation → selfpollination of hybrid offspring → second filial generationii. second filial generation → self-pollination of hybrid offspring → crosspollination of pure organisms → first filial generationiii. cross-pollination of pure organisms → second filial generation → selfpollination of hybrid offspring → first filial generationiv. self-pollination of hybrid offspring → first filial generation → crosspollination of pure organisms → second filial generationf. What are the traits of the first filial generation of the pea plant in the experiment carried out by Mendel?i. stem height: tall, flower colour: purple, seed colour: yellow, seed shape: roundii. stem height: tall, flower colour: purple, seed colour: green, seed shape: roundiii. stem height: tall, flower colour: white, seed colour: yellow, seed shape: roundiv. stem height: short, flower colour: white, seed colour: green, seed shape: wrinkled

90 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 91g. Two organisms of the same species with contrasting characteristics are crossed. The first one is the black mouse the dominant one and another one the white mouse is the recessive one. Now, observe the concept map below. What is the colour of A?A B pair with recessive genepair with dominant geneDominant gene i. black ii. white iii. hybrid black iv. hybrid white h. A cross between pure black pigs and hybrid black pigs is shown in the phylogenetic chart below. Write its genotype. Pure black pigs hybrid black pigs BB Bb Gametes B B B b BB Bb BB Bbi. black : white = 2:2ii. black: white = 3: 1iii. pure black: hybrid black: pure white = 1:2:1 iv. pure black: hybrid black = 2:2 i. Observe the conversation and select the best option. Arya: No dwarf plants are seen when pure tall pea plants and pure dwarf pea plants are crossed in the first filial generation. Elle: The characteristic of being a dwarf is lost forever. It will never appear again.Eleonor: The characteristic of being a dwarf is not lost. It can appear again in other generations. i. Arya is wrong. Elle and Eleonor are correct. ii. Elle is wrong. Arya and Eleonor are correct. iii. Eleonor is wrong. Arya and Elle are correct. iv. All are correct. No one is wrong. j. If a white-flower pea plant is born from the breeding of two red-flowered pea plants, what type of pollination is done during this experiment? What generation do these parents belong to? i. Self-pollination is performed. These parents are the first filial generation.ii. Cross-pollination is performed. These parents are second filial generation.iii. Self-pollination is performed. These parents are second filial generation.iv. Cross-pollination is performed. These parents are the first filial generation.

92 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 93a. i b. ii c. ii d. ii e. i f. i g. i h. iv i. ii j. iAns of MCQSTEP22. Very short questions a. Mendel did not do his experiment in frogs instead of peas. Give reason. b. A male and a female drosophila were crossed to produce four offspring. The observations are listed below. Which law of inheritance is related to this table?Traits Long wing Short wingObservation Seen in three of them Seen in one of them c. Write the dominant traits of a pea plant. d. Write the characteristics of the second filial generations of Mendel’s experiment. e. What is the genotypic ratio of the second filial generation during the monohybrid cross of pure red-flowered pea plant and pure white-flowered pea plant in Mendel’s experiment?f. No white mouse was born when the pure white mouse was crossed with the pure black mouse. What type of hereditary characteristics is the white colour of the mouse? g. Every living being reproduces its own kind of offspring, why?h. If a white dog is born from a black parent, what could be the genotype of the parents?i. What percentage of the offspring will be dominant in the first filial generation and second filial generation, during the monohybrid cross of the pure red-flowered pea plant and pure white-flowered pea plant? STEP33. Short questions a. Write two differences between dominant characteristics and recessive characteristics. b. Show the offspring of guinea pigs obtained by crossing two hybrid black guinea pigs one time. Write the genotype and phenotype. c. When a monohybrid cross between a black male cat and a brown female cat takes place, all the offspring of the F1 generation are black. They do not have brown offspring in the F1 generation, why?d. Which generation is shown here? State the law of heredity that is related to this chart. e. Does the law of heredity apply to human beings too? Explain. f. Is it possible to have a pea plant with a medium height from crosspollination of pure tall pea plant and pure dwarf pea plant? State your view with × B bB BB Bbb Bb bb

92 H eRedity and mendeliSm Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 93reason. g. We can see all phenotypes in the F2 generation, why?h. No two organisms look the same. Give reason. STEP34. Long questions a. Define heredity. State any three significances of Mendalism. b. Prepare a final chart up to the second generation showing the genotype and phenotype of the offspring produced by cross-pollination between red flower pea plants (RR) and white flower pea plants (rr) and write the ratio of the genotype and phenotype.c. Study the given hypothetical situation and answer the following questions.[Mr. Nuhang is a short person. Both of his parents are tall. During his studies in grade 10, he realised that tall characteristics are dominant characteristics. So, he is wondering why he is short. He discussed it with his teacher. He further studied genetics and found out the reasons.]What might be the reasons? Explain with the help of a phylogenetic chart.d. Peas with round seeds and wrinkled seeds are fertilized and the result is shown in the table. Answer the following questions based on the given table.i. Write the phenotype and genotype ratio of round peas and wrinkled peas in that generation.ii. Both laws of dominance and law of segregation hold on to that result, how?e. Clarify the law of dominance and purity of gamete with the help of an example.Project Work1. Make a profile of your dominant and recessive characteristics of different traits like hair type, thumb, chin, tongue, cheek, colour of eye, hand and earlobe of your friends.2. Visit a pea garden and observe the contrasting characteristics of the pea plants.♦♦♦× R rR RR Rrr Rr rr

94 genetic te cHnology Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 95Key terms and terminologies of the unit1. Genes : The genes are the smallest hereditary units present in the chromosomes.2. Genetic engineer : The person who studies about genes of living organisms is called a genetic engineer.3. Genetic technology : The technology in which the genes are cut, modified, deleted, transferred or added is called genetic technology.4. DNA testing : The act of analysing DNA components, sequences or mutations is called DNA testing. 5. Breeding : Breeding is the process by which living things mate and produce their offspring. 6. Selective breeding : The process in which humans identify certain special traits in an organism and take steps to breed them so that a new organism will have those traits is called selective breeding.7. Inbreeding : The act of breeding between males and females who are closely related genetically is called inbreeding.8. Line breeding : The breeding between males and females who are distantly related genetically is called line breeding.9. Cross breeding : If a purebred male and a purebred female of two different species of same genus are crossed to produce new offspring, it is called crossbreeding.Sequence of Curriculum Issued by CDC Introduction to genetic technology Role of DNA tests in various investigations Methods of selective breeding Introduction, examples, merits and demerits of cross-breeding Introduction to the in vitro fertilization and artificial inseminationUNITGenetic Technology4.3Estimated teaching periods Theory Practical4 1Dr. Bhola Rijal, born in July 1948 in Dharan, Nepal, is a distinguished gynecologist and fertility specialist renowned for his pioneering work in reproductive medicine, notably in in vitro fertilization (IVF). Dr. Rijal has played a pivotal role in assisting countless individuals and couples in overcoming fertility obstacles, realizing their aspirations of becoming parents. Dr. Bhola Rijal, About the Nepalese Scientist

94 genetic te cHnology Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 9510. Purebred : If both of the chromosomes of an allele are identical, then the organism is called purebred.11. Crossbreds : The offspring from different species of purebred parents are often called crossbreds.12. In vitro fertilization : In-vitro fertilization is the assisted reproductive technology in which sperm and ovum are harvested, fertilized in a petri dish and then the embryo is introduced in the uterus.13. Artificial insemination : The process in which sperm collected from the desired male is inserted into the reproductive tract of a female at a suitable time is called artificial insemination. 14. Intracervical insemination : If the raw unwashed sperms or donated sperms from a sperms bank is introduced into the vagina it is called intracervical insemination.15. Intrauterine insemination : If the washed sperm is introduced directly into the uterus, it is called intrauterine insemination.Introduction to geneGenes, the fundamental units of heredity, play a pivotal role in shaping our physical traits and behaviours. The smallest units of heredity which are segments of DNA are called genes. They store essential hereditary information, containing codes for the synthesis of proteins that influence our appearance and habits. During sexual reproduction, genes are transferred from parents to offspring, allowing for the reshuffling of genetic material through processes like crossing over. This genetic variation, along with occasional mutations, contributes to the slow evolution of living organisms. The intricate dance of genes during fertilization leads to the creation of new combinations, giving rise to diverse and unique individuals. Understanding the significance of genes is key to appreciating the marvels of heredity and evolution in the biological world. FACTS WITH REASONOffspring obtained from the same parents show some similarities. Offspring obtained from the same parents show some similarities because the genes transfer hereditary characteristics from parents to the children during sexual reproduction.ACTIVITY 1Make a model of RNA and DNA. Genetic technologyGenetic technology is a revolutionary field led by genetic engineers. Genetic engineers are people who are experts in understanding and modifying genes. Genetic technology focuses on the manipulation of genes using biotechnology. This involves modifying, cutting, removing, or transferring genes, a process known as genetic modification. Examples of genetic technology span a wide range, including PCR tests, DNA sequencing, gene therapy, genetically modified organisms and molecular markers in agriculture. Forensic Characteristics of plants and animals can be changed by using the technology called DNA sequencing information in its process, structure and function. MEMORY TIPS

96 genetic te cHnology Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 97science also heavily relies on DNA technology to solve crimes. At the core of genetic technology is DNA, the blueprint of organisms. Editing DNA sequences, involving the addition, deletion, or replacement of nitrogen bases (AT or GC), results in genetically modified organisms with altered characteristics.The significance of DNA in genetic technology cannot be overstated. DNA serves as the foundation for genetic engineering, enabling the manipulation of genes and the development of new traits in organisms. The ability to cut, add, delete and edit DNA has profoundly enhanced our understanding of genetics. Genetic engineering includes transgenic technology, gene expression and molecular markers, finds widespread applications in agriculture, forensic science, and medical fields.The importance of genetic engineering is evident in various aspects of human life. Transgenic technology and molecular markers aid in agricultural advancements, while DNA testing plays a pivotal role in criminal investigations and ancestry identification. Genetically modified crops and animals contribute to the progress of agriculture and animal husbandry, addressing global food demands. Additionally, gene therapy emerges as a promising avenue for treating genetic disorders.While debates surrounding genetic engineering persist, assuming it to be a boon offers compelling arguments. Genetically modified crops have alleviated global hunger, playing a crucial role in sustaining billions. Moreover, the field contributes to medical breakthroughs, producing insulin, vaccines, and life-saving technologies. DNA testing, a key genetic technology, has proven instrumental in solving criminal cases, showcasing the positive impact of genetic engineering. Despite ethical concerns, the overall benefits suggest that genetic engineering is a boon, unlocking numerous possibilities for the betterment of human life.Figure: Inserting gene in a DNAFACTS WITH REASONThe fragment of DNA of one organism is added to the DNA of another organism.The fragment of DNA of one organism is added to the DNA of another organism because it helps to add desired traits in organisms such as increased disease resistance, more food production, survival in extreme weather etc. Genetically modified crops produce large amounts of food. The food is better quality as well. MEMORY TIPS