SGIB3 SB complete bookmarked 051122 - DONT SHARE

SUPERWEEDS! WHERE DID THEY COME FROM? ACTIVITY 1

a. Look at the map. What do you notice?
b. Look at the timeline. What do you notice?
c. Look at the map and timeline together. What observations can you

make?
d. What are the different ways that superweeds could have gotten into

Farmer Green’s corn fields?
3. Share your ideas with the class, according to your teacher’s

instructions. Be sure to update your science notebook. You will refer to
your notes in later activities.

Build Understanding

1. How is a genetically modified organism different from other
organisms?

2. Think about the trends your group discussed when looking at the map
and timeline of superweed reportings. What do you predict will
happen with superweed reports in the next five years among the three
counties?

3. How might genetically modified organisms affect each of the three
pillars of sustainability?
a. Economic
b. Social
c. Environmental

4. Issue connection: What effect might superweeds have on food
sustainability? Explain your reasoning.

KEY SCIENTIFIC TERMS

herbicide
superweed

C-7

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Extension

Superweeds are a real-world problem that is currently debated among
scientists, agricultural boards, and farmers. You can learn more about
this phenomenon by gathering and analyzing data on superweeds in your
local area and/or nationwide. Visit the SEPUP SGI Third Edition website at
www.sepuplhs.org/high/sgi-third-edition for some links. You might also
be interested in learning about new and emerging policies to help mitigate
transgene migration at a national level. Think about what questions you
have, and do additional research to see what you can find out.

C-8

2 Creating Genetically Modified Bacteria

glow-in-the-dark rabbits, pigs, and mice may sound like

something out of a science fiction movie, but because of genetic
modification, these animals actually exist. They are the result of scientists
inserting a gene from the jelly species Aequorea victoria into the animals’
DNA. Genes code for the production of specific proteins. Aequorea jellies
naturally glow in the dark because they have a gene that codes for green
fluorescent protein.

a b
FIGURE 2.1: A gene from an Aequorea jelly (a) has been inserted into the DNA of the
mouse (b), causing it to produce a green fluorescent protein that makes it glow.

C-9

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

In the last activity, you learned that plants can be genetically modified to
have a specific trait, such as herbicide resistance. Farmer Green wondered
if the superweeds growing in his corn fields have the same gene as his
genetically modified corn crops. But how are genetically modified
organisms created in the first place?
In this activity, you will genetically modify a population of Escherichia coli
(E. coli) bacteria. Geneticists study E. coli because even though it is a simple
organism, it uses the same cellular processes to make proteins as do more
complex organisms. You will insert two genes into E. coli: one for green
fluorescent protein (GFP), and one that will make the E. coli resistant to
ampicillin, an antibiotic. Because half the plates on which you will grow the
bacteria contain ampicillin (which normally kills E. coli), only the
successfully modified E. coli will grow on those plates.

Guiding Question

How do scientists genetically modify an organism?

Materials

FOR THE CLASS

spray bottle of disinfectant
supply of paper towels
water bath
ultraviolet light source

FOR EACH GROUP OF FOUR STUDENTS

2 microcentrifuge tubes containing 250 μl of CaCl2
2 sterile toothpicks
2 Luria broth (LB) plates
2 LB-ampicillin plates
3 sterile pipettes
2 sterile spreaders
permanent marker
E. coli starter plate
microcapillary tube and wire with handle
timer
foam floater
microcentrifuge tube containing 500 μl of Luria recovery broth
container of crushed ice

C-10

CREATING GENETICALLY MODIFIED BACTERIA ACTIVITY 2

FOR EACH STUDENT

Student Sheet 2.1, “Genetic Modification Procedure”
Student Sheet 2.2, “E. coli Growth Observations”
Student Sheet 2.3, “Genetics Case Study Comparison”
3 sticky notes
chemical splash goggles

SAFETY

Wear chemical splash goggles when working with chemicals.
Be cautious when working with live organisms. If there are
any spills, or if substances come in contact with your skin, notify your
teacher immediately, and wash with soap and water. Wash your hands
at the end of the investigation. Do not look directly at the ultraviolet
light source, as it might damage your eyes. Follow the sterile
technique practices for working with E. coli.

Procedure

Sterile Technique Practices for Working With E. Coli

1. Keep all equipment away from your eyes and nose to avoid
contact with bacteria.

2. Wipe all surfaces with a disinfectant solution before and after
working with E. coli.

3. W ash your hands before and after any work with E. coli.
4. Treat all equipment that has been exposed to E. coli (pipettes,

spreaders, microcentrifuge tubes, etc.) by soaking it in the
appropriate waste container.
5. To prevent overgrowth of E. coli, do not over-incubate the
culture plates.

C-11

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Part A: Modifying Bacteria

1. Follow your teacher’s instructions for recording notes on this
laboratory.

2. Read the entire procedure to familiarize yourself with the steps. On
Student Sheet 2.1, “Genetic Modification Procedure,” write a summary
of the purpose of this activity and the experimental design you will
follow to transform the E. coli bacteria.

3. Work with your group to sterilize your table surface with disinfectant.
It is important to work on sterile surfaces during this investigation so
that your experiment does not become contaminated.

4. In your group, use a permanent marker to label one of the
microcentrifuge tubes containing CaCl2 “+plasmid” and the other
“Control.” Place both tubes in your container of crushed ice.

5. With the sterile toothpick, carefully scrape away 2 to 4 colonies of ​
E. coli bacteria from the starter plate. To prevent contamination, touch
only the thick end of the toothpick. Be careful not to damage the
surface of the agar while harvesting the bacteria; scrape away only the
bacterial colonies.

6. Place the toothpick with the bacteria into the CaCl2 solution in the
+plasmid tube, and twirl it back and forth in the liquid for a few seconds
to be sure that the bacteria come off the toothpick. Remove the
toothpick, and discard it as instructed by your teacher. Close the tube.

7. Gently flick the end of the closed tube to mix the contents. Your
solution should turn cloudy with E. coli.

8. Repeat Steps 5–7 for the Control tube, using a new sterile toothpick.
9. Obtain the plasmid according to your teacher’s instructions. With a

microcapillary tube, transfer 10 µl of plasmid to the +plasmid tube.
Close the tube. Mix the contents by flicking the tube vigorously with
your forefinger several times, then tap the end of the tube on the table
to make sure that the contents are all at the bottom of the tube. Do not
add plasmid to the Control tube.
10. Place both tubes on ice, and let them sit for 15 minutes.
11. Label the underside of your Luria broth-only (LB-only) plates with
your group’s initials and the date. Label one “+plasmid” and the other
“Control.” Make sure that your labels are small—put them on the
outside edges of the plates so that most of the plate is still easy to see.
Repeat this process with your LB-ampicillin plates.

C-12

CREATING GENETICALLY MODIFIED BACTERIA ACTIVITY 2

12. Prepare to shock the bacteria with heat, which causes the bacteria cells
to take in the plasmid with the GFP gene. Move the tubes from the ice
to the hot water bath as quickly and efficiently as possible. Place both
tubes in the foam floater, then quickly place the floater with the tubes
in the 42°C water bath. Incubate for exactly 90 seconds, and
immediately return the tubes to the ice for 2 minutes.

13. Using a sterile pipette, add 250 µl of Luria recovery broth to each tube,
and mix gently. Cap the tubes. Follow your teacher’s instructions to
incubate the tubes at 37°C for 30 minutes.

14. With a new sterile pipette, transfer 100 µl of the mixture from the
Control tube to the Control LB-only plate. Using the same pipette,
repeat with the Control LB-ampicillin plate. Discard the pipette as
directed by your teacher.

15. Use a sterile spreader to spread the liquid across the entire Control
LB-only plate, taking care not to damage the agar. Using the same
spreader, repeat this process with the Control LB-ampicillin plate. Be
sure to streak the LB-only plate before the LB-ampicillin plate to avoid
contamination. Discard the spreader in the waste container.

16. Repeat Steps 14 and 15, using a new sterile pipette and spreader to
transfer the contents of the +plasmid tube to the +plasmid plates.

17. Let the plates sit for 3 minutes to allow the agar to absorb the liquid
that contains the bacteria.

18. Turn the plates upside down. Your teacher will give you instructions
for incubating the plates. Dispose of all remaining materials as
instructed by your teacher, and sterilize your table surface. Wash your
hands thoroughly with soap and water.

19. On Student Sheet 2.2, “E. coli Growth Observations,” record your
observations of each plate in the column “Time = 0 hours.” With your
group, predict what you expect to see after the plates have incubated.
Be prepared to share your predictions with the class.

20. After 48 to 72 hours, observe the plates under ultraviolet light. Keep
the lids on the plates. Do not look directly at the ultraviolet light source,
as it might damage your eyes. On Student Sheet 2.2, record your
observations of the plates your team prepared in the column
“Time = ___ hours.” Be sure to record the number of bacterial colonies
on each plate and to sketch each plate and the colonies.

21. Follow your teacher’s instructions to compare the results from your
plates with the number of colonies on plates that other groups grew.

C-13

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

22. Dispose of your plates and any other materials as instructed by your
teacher, and sterilize your table surface.

23. Wash your hands thoroughly with soap and water.

Part B: Reading

Throughout this unit, you will read several case studies about genetic
modification. In this activity, you will read a case study about biofuels. You
will use the information you collect on Student Sheet 2.3, “Genetics Case
Study Comparison,” to answer the Build Understanding questions in a
number of activities.
24. Read the case study “Modifying Bacteria to Produce Biofuels,” using

the Read, Think, and Take Note strategy. To do this:
a. Stop at least three times during the reading to mark on a sticky

note your thoughts or questions about the reading. Use the “Read,
Think, and Take Note Guidelines” to start your thinking.

Read, Think, and Take Note Guidelines

As you read, use a sticky note from time to time to:

• Explain a thought or reaction to something you read
• Note something in the reading that is confusing or unfamiliar
• List a word from the reading that you do not know
• Describe a connection to something you’ve learned or read previously
• Make a statement about the reading
• Pose a question about the reading
• Draw a diagram or picture of an idea of connection

b. After writing a thought or question on a sticky note, place it next to
the paragraph in the reading that prompted your note.

c. After reading, discuss with your partner the thoughts and
questions you had while reading.

25. Complete the first row on Student Sheet 2.3, “Genetics Case Study
Comparison.”

C-14

CREATING GENETICALLY MODIFIED BACTERIA ACTIVITY 2

Reading

Modifying Bacteria To Produce Biofuels

To create genetically modified organisms (also known as GMOs),
scientists directly manipulate the genes of an organism, often by inserting
one or more genes from another species, or deleting one or more genes.
The goal is to have a specific effect on the traits of the organism. For
example, inserting a gene might give a plant higher vitamin content.
Deleting a gene might prevent a harmful condition from developing. This
process is called genetic engineering.
When scientists genetically modify an organism, they often insert a gene
from another organism so the modified organism will make a new protein.
The production of a protein in an organism is called gene expression. For
example, the European corn borer is an insect that destroys corn plants by
burrowing into the stem, causing the plant to fall over. There is a
bacterium, Bacillus thuringiensis, that produces a protein that kills the
larvae of the corn borer and other insects in its family. Scientists have
genetically modified a strain of corn using the gene from the bacteria so
that the corn produces the larvae-killing protein.
There are many reasons that scientists might want to genetically modify an
organism. For example, bacteria can be modified to produce human
insulin that can treat patients with diabetes, or to produce an enzyme that
helps break down oil, which can help clean up oil spills.
One area that scientists are researching is the use of genetically modified
organisms to produce alternatives to fossil fuels. One alternative is a group
of fuels called biofuels. Biofuels, including bioethanol and biodiesel, are
compounds that are produced from renewable biological sources. Plants
high in starch and sugar are made into bioethanol, while vegetable oils and
other fats are made into biodiesel. Both of these fuels may be burned in
combustion engines in place of
fossil fuels. Research on
alternative fuels and the use of
genetically modified organisms
to produce them is rapidly
expanding.

FIGURE 2.2: Many farm machines
at the Agricultural Research
Service’s Beltville Agricultural
Research Center are running on a
mixture of diesel fuel and biodiesel,
which is made from soybean oil.

C-15

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Scientists are working on ways to make the production of biofuels
sustainable. They want to improve the plants to increase how much fuel
they can produce, and to improve the technology for extracting fuel from
the plants. Much of the research focuses on developing genetically
modified microorganisms, such as yeast and bacteria. Currently, most
bioethanol is made by using microorganisms to ferment corn or sugarcane.
The starchy and sugary edible parts of these plants are the parts used to
make bioethanol with current methods. If too many farmers dedicate too
much agricultural land to producing biofuel plants, supplies of basic foods
will shrink. If nonagricultural land is converted to grow biofuel, natural
habitat is lost. Some scientists are working on making genetically modified
microorganisms that are able to efficiently use the waste stalks and leaves of
crops, instead of the edible parts. Other scientists are looking at how to
make biofuel from other crops, like grasses, that don’t require the higher-
quality soil that food crops need.
Using grasses and inedible parts of crops poses a big challenge. They
contain two substances: lignin and cellulose. These substances add strength
to the plants’ cell walls but are very hard to break down to make biofuels.
The solution might be found in bacteria that already exist. Bacteria that live
in compost piles or in the digestive systems of termites and other
organisms produce enzymes that break down wood and the tough parts of
plants. Scientists are working to insert genes from these bacteria into other
bacteria, like E. coli, that grow well on the large scale needed for producing
biofuels. Scientists hope to genetically modify a strain of E. coli that can
break down the lignin and cellulose and convert them into ethanol.

Physical pre-treatment, Fuel-producing
chemicals and enzymes microorganisms

Solar energy Feedstock Sugars Biofuels

aFInGdUtRhaEedPad2lad.i3ntdi:toisStniouoolsnaefromsefonimclearirorcgoeryonrgioesraruggnsayiesndmtiosbsmc,yrpspe,lalapatnlneattnsssututsgoguaacgrrrsase.racTsathecnraosbnuuegbgafeherfsrpem.hrTmeyhsnreiotcneuatdegl dphtortpoophcpryeorssodiscdiuanuclgcepearbonbicdoioeftfsuuhseieenllssg..

C-16

CREATING GENETICALLY MODIFIED BACTERIA ACTIVITY 2

Another potential use of genetically modified microorganisms is to
improve the quality of the fuel produced from sugars. Typically, yeast or
bacteria break down sugars and starch to produce ethanol, but ethanol
doesn’t have a high energy content. It also binds to water and corrodes
metals, including those used to make storage tanks and gas tanks in cars.
One research group has modified E. coli to produce fuels, such as butanol,
that store more energy than ethanol, are easier to separate from water, and
perform better in engines.
Currently, other types of microbes can produce these preferred fuels, but
the yield is low. These fuels can also be produced through breaking down
the plant matter with chemicals, but this is expensive and requires a lot of
energy. In order to modify E. coli to produce these fuels, scientists deleted
several genes in the E. coli and replaced them with genes from other
organisms. These efforts have been somewhat successful. The modified
E. coli produces the preferred fuels, but not enough for commercial use.
Scientists are continuing to work on modifying E. coli to maximize
production of the fuels. They are also investigating similar genetic
modification techniques in yeast and other microbes that are often used
to produce other types of biofuel.
Some scientists question the safety of modifying bacteria and other
microbes to produce biofuel. They think that there has not been enough
safety testing done on genetically modified organisms, and they are
concerned that there may be unintended consequences for human health
or the environment. Although the E. coli needed to make biofuels would be
grown only in laboratories, there might be problems if some were
accidentally transferred to other environments.

FIGURE 2.4: Biofuel-powered vehicles are now available to consumers. These vehicles
run on ethanol that is commonly made from corn or sugarcane.

C-17

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Alternatives to developing genetically modified organisms for producing
biofuels include:

• Improving the fuel quality of plants by selective breeding
• Weakening plants’ cell walls through selective breeding
• Improving the process of chemically breaking down plant matter

Both scientific advances and policy decisions will play a role in decisions
about pursuing these approaches to producing biofuels.

FIGURE 2.5: These mosquito
larvae have been genetically
modified with GFP. Scientists
hope to one day genetically
modify mosquitoes so they
cannot carry the protozoa that
cause malaria. This could save
millions of lives.

Build Understanding

1. Construct an explanation about what happened to the E. coli that you
modified. In your response, address the following questions:

• How did you change the DNA of the E. coli?
• What happened to the E. coli after you inserted the GFP and

ampicillin resistance genes?

• How do you know if the genetic modification worked?
• How would you know if the modification did not work?

2. A group of students just completed the genetic modification of E. coli,
as you did in this investigation. However, their results were very
different than expected. E. coli overgrew the surface of each plate, and
no individual colonies were visible on either plate. Explain what could
have happened and how the students could solve this problem.

C-18

CREATING GENETICALLY MODIFIED BACTERIA ACTIVITY 2

3. How might the genetic modification of E. coli be similar to the genetic
modification of crops, like Farmer Green’s corn, for herbicide
resistance? Explain your reasoning.

4. What are the possible trade-offs involved in developing genetically
modified organisms to produce biofuels?

KEY SCIENTIFIC TERMS

biofuel
DNA
gene
gene expression
genetic engineering
genetically modified organisms (GMOs)

Extension: Engineering Connections

The Zika virus is transmitted by mosquitoes. The virus normally causes
only mild illness, but it can cause severe birth defects if a pregnant woman
becomes infected. How can genetic engineering be used to combat
infectious diseases like the Zika virus? Visit the SEPUP SGI Third Edition
website at www.sepuplhs.org/high/sgi-third-edition to read articles about
how scientists genetically modify mosquitoes in a lab setting to help
control wild mosquito populations. Think about what questions you have,
and do additional research to see what you can find out.

C-19



3 Mitosis and Asexual Reproduction

when scientists genetically modify an organism, it is important
that they are able to predict how many of the offspring of the modified
organism will contain the newly inserted gene. In the case of herbicide
resistant crop plants, scientists want the offspring to have the trait so that
future generations of the plant are also herbicide resistant. Being able to
predict how many offspring contain a newly inserted gene depends on how
the organism reproduces.

FIGURE 3.1: E. coli bacterium in the early stages of reproduction

Mitosis is the process by which a single cell divides to produce two
identical daughter cells. In mitosis, a parent cell replicates its DNA and
forms new daughter cells. When plants, animals, and other multicellular
organisms grow, their new cells are also products of mitosis.

C-21

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

In this activity, you will investigate how a single-celled organism—in this
case, E. coli—reproduces by mitosis. You will model mitosis and compare
the genetic makeup of a parent cell and its daughter cells. Finally, you will
predict the chance of an inserted gene being passed on to the next
generation.

Guiding Question

If a genetically modified cell undergoes mitosis, how likely is
it that the daughter cells will inherit the inserted gene?

Materials

FOR EACH PAIR OF STUDENTS

pop-beads chromosome model set:
16 blue pop beads
16 green pop beads
2 orange pop beads
2 blue centromeres
2 green centromeres

computer with Internet access

FOR EACH STUDENT

Student Sheet 3.1, “Mitosis”

Procedure

Part A: Simulating Mitosis

1. Visit the SEPUP SGI Third Edition page of the SEPUP website at
www.sepuplhs.org/high/sgi-third-edition. Follow your teacher’s
instructions to open the simulation. Determine what happens to the
genetic material of the cell at each phase.

2. In the middle column of Student Sheet 3.1, “Mitosis,” draw what
happens to the chromosomes during each phase of mitosis.

3. In the third column of Student Sheet 3.1, summarize the key events of
each phase of mitosis.

C-22

MITOSIS AND ASEXUAL REPRODUCTION ACTIVITY 3

Part B: Modeling Mitosis

4. With your partner, use the pop-beads chromosomes model to show
what happens when a cell with one pair of chromosomes undergoes
mitosis.
a. Make two strands of four blue pop beads, and attach one strand
to each end of a blue centromere. Repeat this process for the
green beads. This represents one pair of chromosomes before
they replicate.
b. Simulate the replication of each chromosome during interphase.
To do this, repeat Step 4a. With the centromeres, form the shape of
a replicated chromosome as shown in Figure 3.2. Note that the X
shape is a replicated chromosome and that the model demonstrates
one pair of replicated chromosomes.

FIGURE 3.2: This model shows one pair of replicated chromosomes.
3422 SEPUP SGI Genetics SB

c.AF iggReunreedf:a3eM4r2e2tdGoCeonSnStdBu90/d39_e0n2 t Sheet 3.1 to determine how to move the
chromosomes as they would move through each phase—prophase,
metaphase, anaphase, and telophase. Determine the genetic
makeup of the cells that result.

C-23

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Working with Pop Beads

Pop beads may be difficult to put together and pull apart, particularly if
they’re new. If this is the case, try these tips:

• To remove pop beads from a chain, pull the beads straight apart.
• Do not bend the peg connecting the pop beads, or it may break.
• Try swapping one pop bead for another one in your set.
• To put beads together, wet the ball and peg with a small amount of water.
• As a last resort, ask your teacher to provide a tiny amount of mineral oil

or petroleum jelly, and rub it on the ball and peg of the beads.

5. With your partner, discuss how the genetic makeup of the daughter
cells compares to that of the parent cell. Write your conclusions in
your science notebook.

6. Consider a cell that has been genetically modified and has had a gene
inserted into one chromosome. Starting with a pair of unreplicated
chromosomes, replace one of the blue pop beads on one model
chromosome with an orange pop bead. With your partner, repeat
Steps 4 and 5 for your modified model chromosomes to demonstrate
the replication of the modified chromosome.

7. Discuss with your group the probability of a daughter cell receiving an
inserted gene from a genetically modified parent cell that undergoes
mitosis. Be sure to include the following structures in your discussion:

• chromosomes
• parent cell
• daughter cell
• gene

8. Write your conclusions in your science notebook.

C-24

MITOSIS AND ASEXUAL REPRODUCTION ACTIVITY 3

Build Understanding

1. Using your model on Student Sheet 3.1, explain the process of mitosis.
In your explanation, include the preparations that take place during
interphase and each of the four phases of mitosis (prophase,
metaphase, anaphase, and telophase).

2. In mitosis, how does each daughter cell’s chromosomes compare to the
chromosomes of the parent?

3. A friend of yours claims that every genetically modified single-celled
organism that reproduces asexually would pass along the inserted gene
to its daughter cells. Based on your work in this activity, is your friend’s
claim accurate? Explain.

4. Issue connection: If a plant is genetically modified to be herbicide
resistant, would you expect all of its cells to have this modification?
Would you expect all of its offspring to have this modification? Explain
your reasoning.

KEY SCIENTIFIC TERMS

asexual reproduction
centromere
chromatid
chromosomes
daughter cells
mitosis
parent cell

C-25



4 Breeding Corn

farmers throughout the world grow crops and raise animals to
feed their families and communities. Livestock and most crops reproduce
by sexual reproduction, in which two parents contribute genetic material
to the offspring. Farmers practice selective breeding to improve their
livestock and crops. In selective breeding, organisms with desirable traits
are mated with the goal of producing even more desirable offspring. For
example, farmers have bred apples for different colors, tastes, and types of
consumption, such as baking, juicing, and eating. Animals, such as
chickens, are also bred using selective breeding. Some chickens are bred for
laying eggs, and others are bred for meat. Many varieties of egg-laying
chickens have been bred to produce eggs of different colors and sizes.

FIGURE 4.1: Selective breeding has produced chicken breeds that lay eggs with a variety
of colors and sizes.

C-27

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Before there were genetically modified organisms, selective breeding was
the only way that people could develop varieties of crops and livestock
that had traits they wanted or needed. Selective breeding allows farmers
to optimize crop production so that only the most desirable plants are
grown. This practice supports the economic sustainability of food
production. In this activity, you will explore the results of selectively
breeding two varieties of corn.

Guiding Question

How can information about the genetic makeup of plants
help farmers predict what genes crops will inherit?

Materials

FOR EACH PAIR OF STUDENTS

2 P allele cards
2 p allele cards
cardboard corn ears A and B

FOR EACH STUDENT

Student Sheet 4.1, “Traits and Heredity”

Procedure PARENT GENERATION

Part A: Traits and Heredity plant that produces plant that produces
purple kernels yellow kernels
1. Read the questions posed on
Student Sheet 4.1, “Traits and
Heredity.” Fill in the “I think . . .”
column with a response to each
question.

2. With your group, discuss what
you think is happening in the
cross shown in Figure 4.2.

FIGURE 4.2: When a corn plant that produces ears with purple plant that produces
kernels is crossed with a corn plant that produces ears with yellow purple kernels
kernels, the resulting offspring have ears with only purple kernels.

3422 SEPUP SGI Genetics SB
Figure: 3422GenSB 04_04
Agenda MedCond 9/9
C-28

BREEDING CORN ACTIVITY 4

3. Share your ideas with the class, as directed by your teacher.
4. Read the following text, “Basic Genetics.”

Basic Genetics

• A n organism has two copies of the gene for each of its traits. These

copies are called alleles.

• Some traits are dominant, meaning that they will mask another

version of the trait, or they are recessive, meaning that they will be
hidden by a dominant trait.

• I n scientific writing, a dominant trait is represented with a capital

letter, which is underlined to be easy to distinguish. A recessive trait
is shown with a lowercase letter.

• In the corn example, the allele for the purple kernel color is P, and the

allele for the yellow kernel color is p. The possible allele combinations
for a corn plant are PP, Pp, and pp.

5. With your partner, use the P and p allele cards and what you know
about the heredity of traits to discuss why the corn kernels (offspring)
were all purple. Discuss your ideas with the other pair in your group.
Record a summary of your discussion in your science notebook.

6. Record your group’s ideas from Step 5 in the “My group thinks . . .”
column of Student Sheet 4.1. You will return to these questions later to
see how your ideas and understanding of traits and heredity have
changed.

7. Use the information in “Punnett Squares” to answer this question:
What is the ratio of purple to yellow offspring?

C-29

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Punnett Squares

A Punnett square is a tool that shows and helps predict the possible
offspring when two organisms reproduce sexually. This Punnett square
shows a cross between a purple corn plant that has PP alleles and a yellow
corn plant that has pp alleles.

PP

p Pp Pp

p Pp Pp

FIGURE 4.3: PP x pp
F3i4gT2u2hreeS:Ea3P4lUl2eP2leGSsGenwI GSrBeitn0te4et_nic0sa5SloBng the top and side of the square are the alleles from
Ageeancdha pMaerdeCnotnodr9g/a9nism—in this case, the purple corn and the yellow corn.

The allele combinations inside the square show the possible combinations
that could be found in the offspring of this cross.

8. Draw a blank Punnett square in your science notebook, and show what
a cross would look like between two parent corn plants with the genes
Pp. Note the allele combinations and what color the offspring would
be for each combination.

9. Determine the predicted ratio of the different-colored offspring in the
Punnett square you drew in Step 8. How is this different from the ratio
for the Punnett square shown in Step 7?

C-30

BREEDING CORN ACTIVITY 4

Part B: Counting Kernels

10. Read the following scenario:

Shauna is a gardener who would like to produce bicolored (two-colored)
corn like some samples she got from a friend. In her garden, she has corn
with purple kernels and corn with yellow kernels, but no bicolored corn.
Shauna begins by crossing the plants with yellow kernels with those with
purple kernels. The offspring produced all have purple kernels, as shown
in the Punnett square in Step 7. Help Shauna figure out what to do next
to produce corn like corn ears A and B.

11. In your science notebook, make a data table like Table 4.1.

TABLE 4.1: Corn Breeding Data

NUMBER OF RATIO OF PURPLE RATIO ROUNDED
PURPLE KERNELS NUMBER OF KERNELS TO TO THE NEAREST
YELLOW KERNELS YELLOW KERNELS WHOLE NUMBER

Kernels on ear A
Kernels on ear B

12. Count the number of purple kernels and the number of yellow kernels
on corn ear A. Record them in your data table.

13. Count the number of purple kernels and the number of yellow kernels
on corn ear B. Record them in your data table.

14. With your group, discuss what the ratio of purple to yellow kernels
tells you about the genetic information that was passed from the
parent generation to each of these corn kernels. Remember: In corn,
the trait for purple is dominant over the recessive trait for yellow.

15. From the data you recorded in Steps 12 and 13, calculate the ratio of
purple kernels to yellow kernels. To do this, divide the number of
purple kernels by the number of yellow kernels for each ear of corn.
Enter your results in the data table. Then divide the smaller number by
itself, to produce 1. The ratio of purple to yellow kernels is x :1. Round
the ratio to the closest whole numbers.

16. With your partner, discuss what the genes of the parent corn must
have been to produce the corn kernels on ears A and B. Record your
ideas in your science notebook.

17. Read the next part of the scenario:

Based on the ratio of kernels counted, Shauna constructed the following
three Punnett squares to show the possible crosses she thinks may have
produced the corn on ears A and B.

C-31

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Pp

P PP Pp

P PP Pp

3422 SEPUP SGI GeneticPs SB FIGURE 4.4: Punnett square X—Pp x PP

Figure: 3422GenSB 04_07 p
Agenda MedCond 9/9
Pp
P PP

p Pp pp

3422 SEPUP SGI GenetiPcs SB FIGURE 4.5: Punnett square Y—Pp x Pp

Figure: 3422GenSB 04_08 p
Agenda MedCond 9/9
pp
p Pp

p Pp pp

C-32 FIGURE 4.6: Punnett square Z—Pp x pp
3422 SEPUP SGI Genetics SB
Figure: 3422GenSB 04_09

BREEDING CORN ACTIVITY 4

18. Given the data you collected in Step 12, decide which Punnett square
shown in Shauna’s notes—X, Y, or Z—best describes the cross that
produced ear A. Record your reasoning in your science notebook.

19. Given the data you collected in Step 13, decide which Punnett
square—X, Y, or Z—best describes the cross that produced ear B.
Record your reasoning in your science notebook.

20. Follow your teacher’s instructions to discuss your ideas from Steps 18
and 19 with a partner. Determine if your ideas agree. If not, discuss
why, and try to come to an agreement.

21. Complete the last two columns on Student Sheet 4.1. Follow your
teacher’s instructions for sharing your questions.

22. Read “Probability and Statistics in Genetics.” Discuss with your
partner any questions you have about how probability and statistics
are used in genetics.

Probability and Statistics in Genetics

Statisticians have developed techniques for approximately 0.0001—a highly unlikely
helping scientists determine whether the result. You might start wondering if the
results of an experiment or investigation coin is a double-headed coin!
support or refute their predictions. Think
about tossing a coin. If you toss a coin, the Statisticians take this same approach in
probability that it will land heads is 1 out ​of genetics to determine whether the outcome of
2, or 0.50. If you toss a coin twice, the a genetic cross is due to chance or to some
probability that it will land heads both other factor. Suppose there is an allele for tall
times is 1 out of 4. With 10 tosses, you corn, A, or short corn, a, with the tall allele
would expect that at least 1 toss would land being dominant to the short allele. If two
tails because the probability that all 10 heterozygous parents are bred, the predicted
would land heads is 1 out of 1,024, or probabilities for genotypes and phenotypes of
their offspring are shown here:

GENOTYPE PROBABILITY PHENOTYPE PROBABILITY A a
AA 0.25 Tall 0.75 A AA Aa
Aa 0.25 Tall 0.75
Aa 0.25 Tall 0.75 a Aa aa
aa 0.25 Short 0.25

FIGURE 4.7: Aa x Aa

C-33

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Probability and Statistics in Genetics continued

If the parents are crossed and produce 100 Statisticians have developed tests to
offspring, the predicted outcome is 75 offspring determine if the observed results are
with the dominant trait and 25 offspring with significantly different from the predicted
the recessive trait. This assumes that an results. These tests are based on the
offspring’s genotype is due to chance. If a cross probabilities of different outcomes. Several
is performed and the observed outcome of calculations are performed that result in a
phenotypes is 76 tall offspring and 24 short statistic (a single value) and the probability of
offspring, this is so close to the expected that value being obtained. In the example
outcome that we can conclude that the result is above (90 tall offspring and 10 short
due to chance. But if the outcome is 90 tall offspring), the probability of obtaining this
offspring and 10 short offspring, the observed result by chance is 0.005, which is very
outcome is much further away from the unlikely. Some other factor is very likely
predicted outcome; we might conclude that affecting the outcome.
some other factor is involved in determining
offspring genotypes and phenotypes.

Build Understanding

1. How does a Punnett square show the possible results of a cross
between two individuals?

2. Describe how your observations of offspring (corn kernels) allowed
you to determine the genetic makeup of the two parents. Include how
you used ratios in this process.

3. What do you predict will happen if a purple corn plant with the genes
Pp is bred with a corn plant with purple kernels and the genes PP?
Explain your answer, and include a matching Punnett square.

4. What might it indicate if the offspring of a cross do not have the
predicted ratio of phenotypes? Include an example in your response.

5. If herbicide resistance is expressed in new weed offspring from one
generation to the next, is the gene modification for herbicide
resistance most likely dominant or recessive? Use Punnett squares to
show an example of how this would work for at least two generations
(in other words, draw at least two Punnett squares).

6. Selective breeding can be beneficial to farmers who are interested in
producing specific varieties of crop plants. What are some possible
environmental trade-offs of selective breeding?

C-34

BREEDING CORN ACTIVITY 4

KEY SCIENTIFIC TERMS

alleles
dominant
Punnett square
recessive
selective breeding
sexual reproduction
trait

Extension

If you would like to learn how to use probability and statistics to determine
if the results of a cross are likely due to chance or some other factor, obtain
Student Sheet 4.3, “Probability and Statistics: Testing a Result Using a
Chi-Square Test,” from your teacher.

C-35



5 Breeding Corn for Two Traits

when farmers breed plants, they often are trying to produce

plants with more than one new, specific trait. For example, a plant can be
modified to resist more than one type of herbicide. But the more traits that
are introduced, the more complicated the breeding becomes. In Activity 4,
you considered the heredity in corn of one trait: kernel color. In this activity,
you will explore patterns of heredity for two traits: kernel color and kernel
texture. You will examine the results of a cross between two purple smooth-
kerneled corn plants. This type of cross is referred to as a dihybrid cross.
You will complete Punnett squares to predict the heredity of these two traits
and compare the predicted and actual results.

FIGURE 5.1: Corn can be bred for various traits. These corn cobs show differences in
kernel color (purple and yellow) and kernel texture (wrinkled and smooth).

C-37

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

How do scientists predict the possible genetic combinations
of offspring for two traits?

Materials

FOR EACH PAIR OF STUDENTS

2 P allele cards
2 p allele cards
2 S allele cards
2 s allele cards
cardboard corn ears C and D

FOR EACH STUDENT

partially completed Student Sheet 2.3, “Genetics Case Study Comparison,”
from Activity 2
3 sticky notes

Procedure

Part A: Punnett Squares for Two Traits

In the crosses that you are about to work with, you will examine kernel
color and kernel texture:

• Kernel color: You will consider two possible alleles—purple (P) and

yellow (p). Purple is dominant over yellow.

• Kernel texture: You will consider two possible alleles—smooth (S) and

wrinkled (s). Smooth is dominant over wrinkled.

1. With your partner, use the P/p and S/s allele cards to model the sex
cells (gametes) that might be produced by parents with purple smooth
kernels and the genotype PpSs (heterozygous for both traits). Record
each possible gamete in your science notebook. (Remember, each
gamete should include one of the alleles for the gene for color and one
of the alleles for the gene for smoothness.)

C-38

BREEDING CORN FOR TWO TRAITS ACTIVITY 5

2. Follow your teacher’s instructions for copying the Punnett square
shown here. Write the possible allele combinations you determined in
Step 1 on your Punnett square in place of the dotted blanks.
Parent 1: P p S s

Parent 2: P p S s

FIGURE 5.2: PpSs x PpSs

3422 SEPUP SGI Genetics TG

3. CoFimguprele: te this Punnett square for the cross described in Step 1.
4. Use your Punnett square to answer the following questions:

a. How many genotypes are possible in the kernels produced by the
cross in Step 1?

b. How many phenotypes are possible in the kernels produced by the
cross in Step 1?

Record your answers in your science notebook.
5. Use your Punnett square to predict the ratio of phenotypes for the

cross you performed in Step 1. Express your ratio in this form:
# purple smooth : # purple wrinkled : # yellow smooth : # yellow wrinkled
Record your ratio in your science notebook.

C-39

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

6. In your science notebook, make a data table like Table 5.1.

TABLE 5.1: Corn Cross Offspring Color and Smoothness

NUMBER OF NUMBER OF NUMBER OF NUMBER OF
PURPLE SMOOTH PURPLE WRINKLED YELLOW SMOOTH YELLOW WRINKLED
KERNELS KERNELS KERNELS KERNELS

Ear C
Ear D

7. Obtain ear C from your teacher. This ear is the result of a cross between
two of the PpSs plants you worked with in Steps 2–5. Count the
number of each of the four kernel types found on ear C, and record the
number in your data table. Determine the ratios by dividing each
number by the lowest number in the row, and reduce each to the
lowest ratio.

8. With your partner, determine how closely the ratios of phenotypes
from ear C in your data table correspond to the ratios predicted by
your Punnett square. Discuss the possible reasons for any differences.

9. Imagine that you have several corn plants that have produced only
purple smooth kernels. You want to determine whether these plants
are homozygous (PPSS) for the dominant purple and smooth kernel
traits. What type of cross could you do to find out if your test plants are
homozygous? With your group, develop a plan:

• Record your plan for the cross in your science notebook.
• Predict the phenotypes of the offspring if the test parent plant is

homozygous and if the test parent plant is heterozygous.

• Construct a Punnett square to show the possible results if the test

plants are homozygous (PPSS).

• Describe the genotypes that resulted from the cross, including the

ratios of the results.

10. Imagine that the way you carried out the procedure you proposed for
Step 9 produced corn ears similar to ear D. Obtain ear D from your
teacher. Count and record the number of each type of kernel found on
ear D. Determine the ratios by dividing each number by the lowest
number in the row, and reduce each to the lowest ratio.

11. Analyze the data (the color and smoothness of each kernel) from ear D
to determine if the parent plants are homozygous or heterozygous for
the two traits. Explain your answer in your science notebook.

C-40

BREEDING CORN FOR TWO TRAITS ACTIVITY 5

Part B: Selective Corn Breeding Case Study

12. Individually read the case study “History of Selective Corn Breeding,”
using the Read, Think, and Take Note strategy. To do this:
a. Stop at least three times during the reading to mark on a sticky
note your thoughts or questions about the reading. Use the “Read,
Think, and Take Note Guidelines” to start your thinking.

Read, Think, and Take Note Guidelines

As you read, use a sticky note from time to time to:

• Explain a thought or reaction to something you read
• Note something in the reading that is confusing or unfamiliar
• List a word from the reading that you do not know
• Describe a connection to something you’ve learned or read previously
• Make a statement about the reading
• Pose a question about the reading
• Draw a diagram or picture of an idea of connection

b. After writing a thought or question on a sticky note, place it next to
the paragraph in the reading that prompted your note.

13. When you’ve finished reading, place your sticky notes on the table in
front of you. Share your thinking with your group. Look for
connections between your notes and those of others in your group.

Hint: Did any of you have similar questions? Were people unfamiliar
with the same words? Did people react differently to statements in the
reading?

14. Place your sticky notes in your science notebook. Below them, write a
short summary of what your group discussed and any conclusions the
group came to.

15. Record the appropriate information from your case study on the
second row of Student Sheet 2.3, “Genetics Case Study Comparison.”

C-41

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Reading

CASE STUDY

History of Selective Corn Breeding

Today, the United States grows more corn than FIGURE 5.3: Corn is the most widely grown crop in
any other crop, and produces much more corn the United States.
than any other country in the world. In 2018,
U.S. farmers planted over 90 million acres of feed/residual
corn, resulting in $42.7 billion of profit. The 45.9%
largest percentage of this corn is used for
feeding to livestock. The remainder is for
human consumption, corn-based biofuel, and
other products, including cornmeal, corn oil,
cornstarch, high-fructose corn syrup, fuel
alcohol, beverage alcohol, and corn feed. The
ups and downs of corn-crop yields from year
to year have a major impact on the U.S.
economy and the availability and cost of food.
Growing all this corn also has a major
environmental impact.

Corn has been grown in southern Mexico for
more than 6,000 years. Both anthropological
and genetic evidence suggest that corn is
descended from the wild grass teosinte. Teosinte
is native to Mexico and parts of Central
America; it produces small hard kernels that

export ethanol
18.9% 24.7%

seed starch high fructose
0.2% 2.1% corn syrup
sweeteners 3.9%
alcohol 1.8%
1.0%

cereal/other
1.5%

FIGURE 5.4: Teosinte plant FIGURE 5.5: This chart shows how much of the U.S. corn
C-42 crop is used for various products.

BREEDING CORN FOR TWO TRAITS ACTIVITY 5

people once cooked and ate. Some scientists People farming teosinte began to purposefully
think that the selective breeding of teosinte by select and breed plants with desirable traits.
native Mexican farmers eventually produced They cultivated plants that produced more
plants that we would recognize today as corn. kernels per cluster and were resistant to drought
and disease. Over the centuries, farmers
The differences between corn and teosinte are continued to select and breed the plants with
remarkable. Teosinte produces ears with a few traits that best suited their needs. As humans
seeds that each have a hard outer coating and took the plants throughout North America,
are easily separated. In contrast, the corn you they selected plants that grew faster in the
are familiar with produces hundreds of kernels shorter summers and could withstand drought,
per ear. These kernels are much larger, softer, whereas farmers who carried corn to the
and sweeter than teosinte kernels. Without Caribbean islands selected plants that could
human cultivation, current-day corn kernels withstand heavy rainfall.
would remain attached to the cob and would
not be dispersed or able to produce new plants. Today, because of human manipulation, there
are hundreds of varieties of corn. One type may
At some point, humans started to farm be 2 feet tall while another grows to 12 feet tall.
teosinte for food and other purposes. Ears range from 1 to 18 inches long. Some types
Anthropologists hypothesize that mashed dried grow with as little as 5 inches of rain in a
kernels were used as a type of a baby powder growing season, and others thrive in as much as
and as a healing substance. The leaves of 150 inches of rain in a growing season.
teosinte have high sugar content and may have
been chewed like chewing gum.

FIGURE 5.6: Farmer in a field of corn. FIGURE 5.7: At the top is a Teosinte ear (Zea mays
ssp. mexicana). At the bottom is an ear of modern
corn. In the middle is the F1 hybrid of these two
species from the University of Wisconsin–Madison.

C-43

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Corn became a key crop in the United States purposes, such as feed corn or biofuel corn.
in the mid-1800s as settlers’ push westward New genetic technologies have led to further
vastly increased farmlands. Farmers continued improvements in selective breeding. One such
to selectively breed corn for desirable traits. development is the mapping of the corn genome
For example, some developed plants with low completed in 2009. A genome is the complete
moisture in their kernels so they would be less sequence of an organism’s genetic material
likely to rot when stored for the winter. Also, (DNA). This map provides the location of each
since each farmer owned a limited amount of gene within corn’s genetic material. This
land and wanted to maximize the yield from information is proving helpful to model the
each plant, they bred plants that produced results of crosses in laboratories. For example,
more ears per plant. In the 1920s, farmers scientists are using the genome map of exotic
began to control which plants pollinated one corn varieties to generate new corn cultivars
another, which allowed them to increase the (cultivated varieties) that can grow in temperate
amount of grain produced per plant. This is U.S. climates and are tolerant of drought and
shown in the graph in Figure 5.8. By the emerging diseases related to climate changes.
middle of the century, this controlled
pollination (instead of natural pollination by With the global population predicted to
wind, rain, and birds) began to show much expand to more than 9 billion people by 2050,
higher yields. Today, an average corn plant in more breeding innovations may also help
the United States produces up to 800 kernels relieve sustainability challenges by enhancing
per ear of corn. not only the yield of corn for human
consumption, but also corn’s use in other
Farmers and agricultural scientists across the products, such as biofuel, textiles, and
globe continue to breed corn for certain renewable fibers.

140 FIGURE 5.8: Pollination graph
2000
Grain yield (bushels/acre) 120

closed-pollinated
100

80
closed-pollinated

60

40 open-pollinated
20

0 1880 1900 1920 1940 1960 1980
1850 Year

3422 SEPUP SGI Genetics SB
Figure: 3422GenSB 07_06
Agenda MedCond 9/9

C-44

Maps1 Maps2 Maps3 Maps4 Maps5

BREEDING CORN FOR TWO TRAITS ACTIVITY 5

Build Understanding

1. Use the terms allele, genotype, phenotype, and offspring to describe the
information given in the Punnett square in Figure 5.9.
Rr

R RR Rr

r Rr rr

FIGURE 5.9: Rr x Rr

2.3Fi4 gCC2u2ooremSr:En3Pp4Uwa2Pr2ietGShGethnItGhSeBeePn0Pue6tu_nic0nns4neSteBtttsqsquuaraersesyoyouucoconnstsrtuructcetdedininAtchtiisviatcyti4v:iBtyr.eeding
Agae.n dHa MowedCdoidndy9o/u9 need to change the Punnett square to consider two
traits?
b. How would you need to change the Punnett square if you were to
consider three traits?

3. Issue connection: You are a farmer selecting a herbicide resistant corn
to plant on your farm. What are the advantages and trade-offs of
selecting a corn that is resistant to more than one type of herbicide?

4. If herbicide resistance is a dominant trait, what is the likelihood of
offspring receiving that trait if one parent is homozygous for the trait
and the other parent is not herbicide resistant? What if one parent is
heterozygous for the trait and the other parent is not herbicide
resistant?

5. In some cases, superweeds have more than one gene for herbicide
resistance. If a superweed has two different genes for herbicide
resistance, and it breeds with a plant that does not have any herbicide
resistance, what would the genotypes of their offspring be? Use a
dihybrid Punnett square to predict the results of this cross. Assume
that any genes for herbicide resistance are dominant.

C-45

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

6. Table 5.2 lists the reproductive characteristics of three organisms. In
the context of selective breeding, explain why a geneticist would need
to understand each of these characteristics.

TABLE 5.2: Reproductive Characteristics of Three Organisms

ORGANISM MODE OF AGE OF SEXUAL TOTAL POSSIBLE NUMBER OF
Rice plant REPRODUCTION MATURITY OFFSPRING PRODUCED PER
Corn plant sexual reproduction 2–3 months REPRODUCTIVE CYCLE
sexual reproduction 2–3 months 50 grains (seeds)
Cow Up to 800 kernels (seeds) per ear
sexual reproduction
1 year Note: Sweet corn has been bred to
produce up to 6 ears per plant.
Mainly 1

7. Which method do you think is better for producing new varieties of
food crops: selective breeding or genetic modification? Why? What
questions do you still have about these methods?

KEY SCIENTIFIC TERMS

allele
dihybrid cross
gamete
genome
genotype
phenotype
Punnett square
selective breeding
trait

C-46

6 How Did This Happen? Class Consensus

for centuries, selective breeding has been an effective method

for people to generate food crops with beneficial traits. However, one
significant trade-off is the amount of time required to achieve the desired
results. Since the 1990s, genetic engineering of crop plants has significantly
reduced the time required to produce food with specific traits. As more
and more genomes are mapped for different organisms, genetic
engineering has more specific methods for changing crop production.
So far in this unit, you have learned how scientists use genetic engineering
to modify organisms—such as E. coli and corn—to produce a desired trait,
how modified genes are passed to daughter cells through asexual
reproduction and mitosis, and how selective breeding has been used to
improve the quality of crops. In this activity, you will apply what you’ve
learned to the case of Farmer Green and the superweeds he found in his
corn fields, and you’ll identify any questions you still have about what may
have happened.

FIGURE 6.1: Genetic engineers grow genetically modified plants in laboratory experiments
to measure their traits, such as rate of growth, drought tolerance, and herbicide resistance.

C-47

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

Why isn’t herbicide working on the weeds in Farmer Green’s
corn fields?

Procedure

1. In your group, discuss your answer to the guiding question, supporting
your answer with evidence as well as your own opinions.

2. Pair up with a student from a group other than your own. Take turns
sharing your group’s ideas from Step 1. Discuss what is similar and
different between your ideas. Be prepared to share your thinking with
the class.

3. Follow your teacher’s instructions to share ideas from your discussion,
including things that you and your partner agreed and disagreed about.

4. In your science notebook, record what you have learned since you
completed Activities 1–5 and what questions you still have about how
superweeds may have gotten into Farmer Green’s fields.

5. Follow your teacher’s instructions for sharing your responses to Step 4.
6. Write your own response to the guiding question in your science

notebook. Record any questions you still have about how superweeds
got into Farmer Green’s corn fields.

Build Understanding

1. Farmer Green claims that superweed seeds must have contaminated
the seeds he used for planting his crops. Do you agree or disagree with
his claim? What is your evidence and reasoning?

2. In Activity 5: Breeding Corn for Two Traits, you compared your
predicted ratio of offspring to the actual results of a dihybrid Punnett
square cross for two traits in corn.
a. How did your results differ from the actual results? Why do you
think the results differed from your prediction?
b. Suppose that you tested the resistance of 1,000 corn plants against
two different herbicides (A and B). You know that the gene for
resistance to each herbicide is dominant and that the parent corn
plants are heterozygous for each herbicide resistance gene. What
results would you predict?

C-48

HOW DID THIS HAPPEN? CLASS CONSENSUS ACTIVITY 6

c. Compare your prediction to the results in Table 6.1. How do these
observed results compare to your predicted outcomes? How could
you tell if the outcomes are by chance or are due to some other
factor? What other factors might affect the outcomes? (Suggest at
least three.)

TABLE 6.1: Test Results

TOTAL PLANTS RESISTANT TO A RESISTANT TO A, RESISTANT TO B, NONRESISTANT
AND B NONRESISTANT NONRESISTANT TO A AND B
1,000 TO B TO A
438 63
375 124

KEY SCIENTIFIC TERMS

genetic engineering
genome
phenotype
Punnett square
selective breeding
trait

C-49



7 Protein Synthesis:
Transcription and Translation

Investigative Phenomenon

After Farmer Green found superweeds in his pass on their modified genes to their
corn fields, he learned that several other offspring—but he isn’t sure if they can pass
farmers in surrounding counties have modified genes to other plants in their
reported superweeds in their fields. He’s also environment. Could superweeds have
read newspaper articles about superweeds inherited the herbicide resistance gene from
being a problem in farms across the country; crops? To fully understand how the
other farmers are complaining that the superweeds in his fields became herbicide
herbicides they’ve been using to control resistant, he needs to know what was
weeds for many years are no longer working. happening at the level of their DNA. Do the
One article mentions that farmers are superweeds have the same herbicide
perplexed by the pattern of these weeds resistance gene as his crops?
appearing. The weeds seem to be popping
up independently in different locations far FIGURE 7.1: Genetically modified corn crop
apart from one another, not spreading out
from one location. Farmer
Green is confused about why
this is happening and why
superweeds are taking over
his fields. He wonders how
superweeds become resistant
to a herbicide.

Farmer Green knows that
genetically modified crops, like
herbicide resistant corn, can

C-51

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Genes carry the information that, along with environmental factors, FIGURE 7.2: Genes
determines an organism’s traits. How does this work? Although the complete determine proteins,
answer to this question is complex, the simple answer is that genes direct the which determine traits.
production of proteins in cells. Proteins are large molecules that the body
uses for a variety of functions. Genes determine what type of proteins are Gene
made. The types of proteins in a cell determine the cell’s and organism’s Protein
structures and functions—in other words, its traits.
When scientists set out to genetically modify an organism, their goal is Trait
often to insert a gene or genes that code for a protein that is not normally
in that organism. In the previous learning sequence, you explored how
genetically modified organisms are generated by modifying bacteria with a
gene that codes for a green fluorescent protein. You also investigated how
selective breeding is used to create crops with desirable traits—like a sweet
taste in corn. Both of these methods manipulate an organism’s DNA so that
the organism produces a specific protein.

Guiding Question LabAids SEPUP SGI Genetics 3e
Figure: Cells 3e SB 07.02
How does a cell make proteins with the information from MyriadPro Reg 9.5/11
DNA?

Materials Maps1 Maps2 Maps3 Maps4 Maps5

FOR EACH PAIR OF STUDENTS c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0

set of 10 Transcription and Translation cards (A–J) c7 m0 y0 k9 c0 m42 y92 k0 c100 m0 y20 k70 c25 m0 y15 k90
bag containing DNA model kit pieces:
c0 m30 y70 k0 c0 m43 y94 k0 c15 m10 y0 k85 c95 m50 y30 ko
36 black deoxyribose sugar pentagons
36 white phosphate tubes c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0 c15 m10 y0 k85 c80 m0 y0 k55 c12 m7 y0 k0 c0 m0 y0 k6
18 white hydrogen bond rods
various orange, yellow, blue, and green nitrogenous base tubes
bag containing transcription model kit pieces:
9 purple ribose sugar pentagons
5 purple uracil nitrogenous base tubes
bag containing translation model kit pieces:
3 purple tRNA molecules (diamond, oval, rectangle)
3 black amino acids (diamond, oval, rectangle)
2 gray polypeptide bond tubes

FOR EACH STUDENT

Student Sheet 7.1, “Transcription and Translation”
Student Sheet 7.2, “Modeling Genetic Modification”
computer with Internet access

C-52

PROTEIN SYNTHESIS: TRANSCRIPTION AND TRANSLATION ACTIVITY 7

Procedure

Part A: Transcription and Translation

Proteins are made in cells by a process called ribonucleic acid, or mRNA. In eukaryotic cells
protein synthesis. Protein synthesis has two (cells with nuclei), transcription takes place in
phases, as shown in Figure 7.3. This process is the nuclei. The second phase of protein
the same in all cells, whether or not the synthesis is called translation, and it happens
organism is genetically modified. on ribosomes in the cytoplasm of a cell. In
this phase, the code in the mRNA messenger
The first phase of protein synthesis is called molecule is translated by transfer RNA
transcription. In this phase, the information (tRNA), which carries the specific amino
contained in DNA is converted into a acids used to make a protein molecule.
messenger molecule called messenger

ribosome

DNA resides in the Transcription: DNA is ribosome Protein is used by the
nucleus. used as a template to Translation: RNA is used as a organism. For example,
make RNA. template to make proteins. an enzyme could be used
by the digestive system.

FIGURE 7.3: Phases of protein synthesis

3422 SEPUP SGI Genetics SB

FAiggeunr ed:1a3.M4 2We2dGiCteohnnSydBo91u/69r_0p1artner, spread out the 10 Transcription and Translation
cards in front of you on the table. Look closely at the cards. Discuss
what each card shows and how the images on the cards differ.

2. Place the cards in the order that you think shows the process of protein
synthesis. Record the order of the cards in Part A of Student Sheet 7.1,
“Transcription and Translation.”

3. With your partner, visit the SEPUP SGI Third Edition page of the
SEPUP website at www.sepuplhs.org/high/sgi-third-edition. Follow
your teacher’s instructions to find the protein synthesis simulation.
View the transcription section of the simulation.

4. Look at the order in which you placed the cards in Step 2. Based on what
you viewed in the simulation, was your ordering of the cards correct?
Discuss with your partner any changes you might need to make. If
necessary, rearrange the cards to reflect the correct order of events in
transcription. Record the revised card order on your Student Sheet.

C-53

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

5. Based on what you observed in the simulation and the information on
the cards, fill in the “Transcription” row in Part A of your Student Sheet.

6. Return to the SEPUP website, and view the translation section of the
protein synthesis simulation.

7. Look at the order in which you placed the cards in Step 4. Based on what
you viewed in the simulation, was your ordering of the cards correct?
Discuss with your partner any changes you might need to make. If
necessary, rearrange the cards to reflect the correct order of events in
translation. Record the revised card order on your Student Sheet.

8. Based on what you observed in the simulation and the information on
the cards, fill in the “Translation” row in Part A of your Student Sheet.

9. Write a description in your science notebook of what is shown on each
card. Be sure to include the name of each molecule involved and a
description of what each molecule does.

Part B: Mutations

As you saw in Part A, protein synthesis begins with the original DNA,
which is transcribed and then translated. Occasionally during this process
a mutation occurs. Mutations are changes in the sequence of nucleotides in
a strand of DNA. Mutations can occur spontaneously or can result from
environmental factors, such as exposure to ultraviolet light or certain
chemicals. In this part of the Procedure, you will investigate the effect of
mutations on protein synthesis.
10. With your partner, review the

information in Part B of Student
Sheet 7.1. Use Figure 7.5 to identify
what the pieces of the model
represent. Select the appropriate
pieces of the DNA model kit, and
build a single strand of DNA, using
the original DNA strand sequence
from the Student Sheet:
5’ TACCTAGCCAGTCGG 3’.

FIGURE 7.4: Mutations can be harmful, neutral, or beneficial.
Certain strains of E. coli bacteria have mutations that allow
them to withstand extreme temperatures.

C-54

PROTEIN SYNTHESIS: TRANSCRIPTION AND TRANSLATION ACTIVITY 7

PROTEIN SYNTHESIS MODEL KEY

DNA Strand RNA Strand DNA Subunit
tRNA
amino acid
anti-codon
phosphate base C
phosphate
base
sugar base G
ribose sugar

base A
base U

Amino Acid Sequence amino acid peptide bond amino acid
peptide bond

FIGURE 7.5: Protein Synthesis Model Key

11. Draw on what you know from Part A of this activity, and use the
model to show translation and transcription for this strand of DNA.
Record your results on Part B of your Student Sheet, using the
information in Table 7.1 to identify the amino acid sequence.

LabAids SEPUP SGI Genetics 3e
Figure: Cells 3e SB 07.05
MyriadPro Reg 9.5/11

Maps1 Maps2 Maps3 Maps4 Maps5

c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0

c7 m0 y0 k9 c0 m42 y92 k0 c100 m0 y20 k70 c25 m0 y15 k90

amino acids with R-groups ( , , )

c0 m30 y70 k0 c0 m43 y94 k0 c15 m10 y0 k85 c95 m50 y30 ko c15 m90 y90 k0 C-55

amino acid

c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0 c15 m10 y0 k85 c80 m0 y0 k55 c12 m7 y0 k0 c0 m0 y0 k6 c25 m0 y15 k90

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

TABLE 7.1: Amino Acid Sequences

U Second letter A G
C
Tyrosine Cysteine
U UUU Phenyl-alanine UCU Serine UAU UGU Stop codon U
UUC Leucine UCC UAC Stop codon UGC Tryptophan C
UCA Stop codon A
UUA UCG UAA UGA G
UUG UAG
UGG U
C
CUU CCU CAU Histidine CGU A
CCC CAC G
C CUC Leucine CCA Proline CGC Arginine
CUA CCG Threonine CAA CGA U
Alanine CAG Glutamine C
First letter CUG CGG A
G
AUU Isoleucine ACU AAU Asparagine AGU Serine
ACC AAC AGC U
A AUC ACA C
AUA ACG AAA AGA A
Methionine AAG Lysine AGG Arginine G
AUG Start codon GCU
GCC
GUU GCA GAU Aspartic acid GGU
GCG GAC
G GUC Valine GGC Glycine
GUA GAA GGA
GAG Glutamic acid
GUG GGG

12. Use the information in Table 7.2 to help you explore how each type of
3Fi4g2u2reS:E3P4U2DP2NGSGeAnI GSmBen1ue6tt_aic0tsi4oSnB affects the production of an amino acid sequence.
Agenda Maed. C Sotnadr9t/w9 ith the original strand of DNA from Step 10.

b. Read the information for the first type of mutation, a base
insertion, and change your DNA strand accordingly.

c. Work through the steps to model transcription and translation of
the DNA. Record the amino acid sequence that results in Part B of
your Student Sheet.

d. Repeat Steps 12a–c for each type of mutation listed in Table 7.2.

TABLE 7.2: SUeCleUcted DNA Mutations

UCC DNSAerine CHANGE IN DNA
CATEGORYUCOAF
MUTATIONUCG CHANGE TO DNA MODEL
Insert a thymine after the first
Base insertion (frameshift) One nucleotide is inserted into cytosine.
the DNA sequence. Delete the first cytosine.

Base deletion (frameshift) One nucleotide is deleted from Change the first cytosine to a
the DNA sequence. thymine.
After TAC, insert three additional
Substitution One nucleotide is substituted nucleotides, CTG.
for a different nucleotide.

Three-base insertion Three nucleotides are added
to or deleted from the DNA
sequence.

C-56