12 Chapter 11 Teacher Copy F5 BI

Jisrun Najaah Fi Ilmi Al Insan Chapter 11: Inheritance

CHAPTER 11

Inheritance

Dan orang-orang yang berkata, “Ya Tuhan kami,
anugerahkanlah kepada kami pasangan kami dan
keturunan kami sebagai penyenang hati (kami), dan
jadikanlah kami pemimpin bagi orang-orang yang

bertakwa
Al Furqan ayat 74

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9.1 MONOHYBRID INHERITANCE
Definition of Monohybrid Cross
1. Involves inheritance of one characteristic
2. Contrasting traits controlled by a gene.

Summary of Mendel monohybrid experiment

1. Trait is controlled by a pair of genetic factors known as allele
2. Pair of alleles segregates (separates) randomly during formation of gametes
3. Only one allele from the pair is found in a single gamete.
4. Zygote formed possesses two alleles (one allele from each parent) for a specific

characteristic during fertilisation
5. Fertilisation is random
6. Genotypic combination which is homozygous dominant shows dominant trait
7. Homozygous recessive shows recessive trait
8. Heterozygous genotype (combination of one dominant allele and one recessive allele)

shows dominant trait.
9. Mendel explained that;

Self-cross of purebreed tall pea plants produce only tall offspring
A pair contrasting traits in pea plant is determined by;

Dominant inheritance factor
Recessive inheritance factor
Dominant inheritance factor suppresses the effect of the recessive inheritance
factor
Recessive trait is not visible although its inheritance factor exists together with the
dominant inheritance factor
10. Mendel introduced Mendel‘s First Law or Law of Segregation which states:

A characteristic of an organism is controlled by a
pair of alleles, and only one of the allelic pair is

inherited in a gamete.

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Key: T - Represents the dominant allele for tall trees
t - Represents recessive alleles for dwarf trees

Parental phenotype

Parental Genotype Tall plant Dwarf plant Mendel crossed a
Meiosis TT tt purebreed tall (TT)
pea plant with a
purebreed dwarf (tt)
pea plant

Gametes TT Cross product in F1
generation consisted
Fertilisation Tt Tt tt
Genotype F1 4 Tt only tall (Tt) pea
All tall plants plants.
Genotype Ratio F1
Phenotype Ratio F1 Shows that the tall trait
Tt Tt (T) is dominant

Dwarf trait (t) is
recessive.

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F1 X F1

Phenotype F1 Tall plant Mendel then crossed
Tt the F1 generation by
Genotype F1 self-pollination (Tt ×
Meiosis Tt).
Gamete X Tall plant
Fertilisation
Genotype F2 Tt
Genotype Ratio F2
Fenotype Ratio F2 Tt Tt

TT Tt Tt tt

1TT : 2 Tt : 1 tt The ratio of tall plant
3 Tall : 1 Short to dwarf plant in F2
generation was 3:1

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11.3 GENES AND ALLELES
Terms Related to Inheritance

Specific location of a gene in J A a K Letters represent genes in
a chromosome (Locus) chromosomes

Gene which located at L
the same locus as the
gene (Allele) BB

C C M Homozygous
dominant allele
Homozygote N
recessive allele dd

Heterozygote allele O Ee
P F f Q Recessive allele

Dominant allele

Terms Meaning
1. Gen
Basic unit of inheritance found on the chromosome
2. Allele Controls specific characteristic of an organism.

3. Homologous Alternative form of a gene for a specific trait
chromosomes Located on the same locus of a pair of homologous
chromosomes.
4. Pure Breed
Chromosome pairs that carry the same trait
Can be present either dominant homozygous (AA) or
recessive homozygous (aa)
Refers to individual which carries two identical alleles for a
trait
Self-cross always produces offspring with the same
characteristics in every generation.

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Terms Meaning
5. Hybrid
6. Heterozygote Product of mating between two purebreed varieties
7. Homozygote
Alleles at loci of a pair of homologous chromosomes are
8. Dominant allele different.
Example, Tt
9. Recessive alleles Both alleles at loci of a pair of homologous chromosomes
are the same
10. Filial Example, TT or tt.
11. Phenotype Allele which always shows its trait when it is present
12. Genotype Suppresses the effect of recessive allele.
13. Characteristic Represented by a capital letter
14. Trait Example, T
Allele which shows its trait when both alleles are recessive
allele.
Effect of recessive allele is suppressed by the presence of
dominant allele.
Represented by a small letter
Example, t.
Refers to a successive generation as a result of mating
between individuals of purebreed parental generation.
• Observable physical characteristic of an organism.
Examples: Flower colour, eye colour, tree height
• Genetic composition of an organism
• Cannot be seen (TT, Tt or tt)
• Heritable feature such as height, eye colour, blood group
and presence of dimples.
• Each characteristic is a feature of an organism.
• Variation of a specific characteristic
• Each inherited characteristic consists of a specific trait.
• Example, height is a characteristic whereas tall or dwarf is
a trait

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Characteristic Trait Genotype Phonotype
Height
Colour Tall TT, Tt Tall
Dwarf tt Dwarf
Blood group Red Red
White RR, Rr White
rr
A A
B IAIA, IAIO B
AB IBIB, IBIO AB
O O
IAIB
IOIO

Summery

• Both alleles are dominant • Both alleles are recessive

(TT) (tt)

• Tall is expressed in • Dwarf is expressed in

phenotype X phenotype

• Both alleles are the same TT tt • Both alleles are the same
(homozygous dominant) Tall Dwarf (homozygous recessive)

• Hybrid produced from • Consists of both dominant allele and
mating of two purebreed recessive allele (Tt)
plants
• Dominant trait for height tall is
• Called the first filial expressed (phenotype)
generation (F1)
• Recessive trait is not observed
Tt

o Suppressed by the dominant
Tall

trait
• Both alleles are different

o Called heterozygote

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Exercise 1:

Black fur in mice is dominant over white fur. What is the ratio of F2 phenotype if purebreed
black fur mice are crossed with purebreed white fur mice?
Key: B Represents the dominant allele for black fur

b Represents recessive alleles for white fur

Parental phenotype

Black fur X White fur
BB bb
Parental Genotype
Meiosis BB bb
Gamete

Fertilisation

Genotype F1 Bb Bb Bb Bb

Genotype Ratio F1 4 Bb
Phenotype Ratio F1 100% black fur baby

1. During formation of gametes, homologous chromosomes separate during meiosis
2. Produce gametes that carry one B allele from black fur and one b allele from white fur
3. Fertilisation between a gamete which carries B allele and a gamete which carries b allele

produces offsprings with genotype Bb in the first filial generation (F1).
4. Since B allele is dominant, the Bb genotype combination expresses only phenotype with

black fur
5. Recessive allele is suppressed by the presence of the dominant allele.

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Self-crossed F1 generation (F1 X F1)
F1 Phenotype

Black fur X Black fur
Bb Bb
F1 Genotype
Meiosis Bb Bb
Gamete

Fertilisation

Genotype F2 B Bb Bb bb
Genotype ratio F2
Phenotype ratio F2 1 BB : 2 Bb : 1 bb

3 black fur : 1 white fur

1. When first filial generation is self-crossed, the second filial generation (F2) will have
offsprings with BB, Bb and bb genotypes

2. BB and Bb genotypes express phenotype with black fur whereas bb genotype expresses
phenotype with white furr

3. Trait that is not observed in the F1 generation (white fur colour) reappears in the F2
generation

4. Ratio in F2 generation is 1 BB : 2 Bb : 1 bb; whereas the phenotypic ratio in F2 generation
is 3 black fur : 1 white fur

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Exercise 1: Punnet Square

Black fur in mice is dominant over white fur. What is the ratio of F2 phenotype if purebreed
black fur mice are crossed with purebreed white fur mice?

Key: B Represents the dominant allele for black fur
b Represents recessive alleles for white fur

Parental phenotype Black fur X White fur
BB bb
Parental Genotype
Meiosis Bb
Gamete
Fertilisation Bb
Genotype F1
Genotype Ratio F1 Bb
Phenotype Ratio F1 100% black fur baby

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Self-crossed F1 generation (F1 X F1)
F1 Phenotype

Black fur X Black fur
Bb Bb
F1 Genotype
Meiosis Bb Bb
Gamete
Fertilisation B b
B BB Bb
Genotype ratio F2 b Bb bb
Phenotype ratio F2 1 BB : 2 Bb : 1 bb
3 black fur : 1 white fur

Notes: For Fertilisation To gamete
1 and 2
From gamete 3 and 4
1 1 and 3
2 2 and 4
3
4

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Exercise 2:
The round seed in the pea bean is dominant over the wrinkle seed. What is the ratio of the F2
phenotype if the purebreed of round seed is crossed with the purebreed of wrinkle seedy?

Key : R Represents the dominant allele for round seed
r Represents recessive alleles for wrinkle seed

Parental phenotype Round seed X Wrinkle seed
RR rr
Parental Genotype
Meiosis R r
Gamete
Fertilisation Rr
Genotype F1 All Rr
Genotype ratio F1 100% Round seed
phenotype ratio F1

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F1 X F1

F1 Phenotype Round seed X Round seed
Rr Rr
F1 Genotype
Meiosis Rr Rr
Gamete
RR Rr Rr rr
Fertilisation
1 RR : 2 Rr : 1 rr
Genotype F2
Genotype ratio F2 75% Round seed : 25% Wrinkle seed
Phenotype ratio F2

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Exercise 2: Punnet Square

The round seed in the pea bean is dominant over the wrinkle seed. What is the ratio of the F2
phenotype if the purebreed of round seed is crossed with the purebreed of wrinkle seedy?

Key : R Represents the dominant allele for round seed
r Represents recessive alleles for wrinkle seed

Parental phenotype Round seed X Wrinkle seed
RR rr
Parental Genotype
Meiosis RR rr
Gamete
Fertilisation Rr Rr Rr Rr
Genotype F1 All Rr
Genotype ratio F1 100% Round seed
phenotype ratio F1

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Self-crossed F1 generation (F1 X F1)

F1 Phenotype Round seed X Round seed
F1 Genotype Rr Rr

Meiosis Rr Rr
Gamete
Fertilisation R r
R RR Rr
Genotype ratio F2
Phenotype ratio F2 r Rr rr

1 RR : 2 Rr : 1 rr

75% Round seed : 25% Wrinkle seed

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11.2 DIHYBRID INHERITANCE
Definition of Dihybrid Cross
1. Inheritance of two characteristics
2. Each characteristic is controlled by a different gene located at a different locus

Mendel’s Second Law
1. Mendel introduced Mendel’s Second Law, also known as Law of Independent Assortment
2. Which states;

During gamete formation, each allele from a pair of alleles can
combine randomly with any allele from another pair of alleles.

Summary of Mendel dihybrid experiment
1. New combinations of characteristics are produced in the F2 generation namely wrinkle

yellow seed and round green seed.
2. Two characteristics (seed shape and colour) are combined in F1 generation but later they

separate and react freely in F2 generation

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Mandel experiment

Pure breed of pea bean round and yellow seed is crossed with pure breed of pea bean wrinkle
and green seed. Using schematic diagram, calculate the ratio F2 phenotype by using Mandel
second law

Key : R Represents dominant alleles for round seeds
r Represents recessive alleles for wrinkly seeds
Y Represents dominant alleles for yellow seeds
y Represents dominant alleles for green seeds

Parental phenotype Round and Wrinkly and
Parental genotype yellow seeds green seeds
Meiosis
Gamete RRYY X rryy

Fertilisation RY RY ry ry

Genotype F1 RrYy RrYy RrYy RrYy
Genotype ratio F1
Fenotype ratio F1 RrYy
All seeds are round and yellow

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Self-crossed F1 generation

F1 phenotype Round and X Round and
yellow seeds yellow seeds
F1 Genotype
Meiosis RrYy RrYy

Gamete RY Ry rY ry RY Ry rY ry

During formation of gametes, any allele for seed shape can pair with
any allele for seed colour.

Punnet squere Male Gamete rY ry
RY Ry RrYY RrYy
RY RrYy Rryy
Ry Female Gamete RRYY RRYy rrYY rrYy
rY rrYy rryy
ry RRYy RRyy

RrYY RrYy

RrYy Rryy

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Genotype F2 Phenotype F2 Genotype F2 Phenotype ratio
F2 ratio 9
3
RRYY 1 3

RRYy Round and 2
RrYY yellow seeds 2
RrYy 4
RRyy Round and 1
Rryy green seeds 2
rrYY 1
rrYy Wrinkly and 2
yellow seeds
rryy Wrinkly and 11
green seeds

Practice 1:

Black fur is dominant over white fur in mice while short fur is dominant over long fur.
What is the ratio of the F2 phenotype when purebreed mice black and short fur crossed
with purebreed mice white and long fur?

Key : B Represents dominant alleles for black fur
b Represents recessive alleles for white fur
S Represents dominant alleles for short fur
s Represents recessive alleles for long fur

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Parental phenotype Black and White and
short fur long fur
Parental Genotype
Meiosis BBSS x bbss
Gamete
BS bs
Fertilisation
Genotype F1 BbSs
Genotype ratio F1
phenotype ratio F1 4 BbSs
100% black and short fur

F1 X F1 Black and X Black and
Phenotype F1 short fur short fur

Genotype F1 BbSs BbSs
Meiosis

Gamete F2 BS Bs bS bs BS Bs bS bs
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Punnet Squere

Male Gamete bS bs
BS Bs BbSS BbSs
BbSs Bbss
Female gamete BS BBSS BBSs BbSs bbSs
bbSs bbss
Bs BBSs BBss

bS BbSs BbSs

bs BbSs Bbss

Genotype Fenotype F2 Genotype Fenotype ratio F2
F2 ratio F2
1 9
BBSS 2
2 3
BBSs Short and 4 3
BbSS black fur 1 1
2
BbSs 1
2
BBss Long and
Bbss black fur 1

bbSS Short and
bbSs white fur

bbss Long and
white fur

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Practice 3 :

The cross of the two oil palm varieties, Dura and Pisifera, produces a new type of oil palm,
Tenera. Tenera has more quality fruit than Dura and Pisifera as in the table below. Self-
crossing among the varieties of Tenera does not produce all the quality offspring as the parent.
Explain why

Key : H Represents the dominant allele for the thick husk
F Represents the dominant allele for the thick kernel
h Represents the recessive allele for the thin husk
f Represents the recessive allele for the thin kernel

Palm Oil Variety Trait characteristics
Fenotype
Genotype

Dura hhFF • Thin husk
• Thick kernel

Pisifera HHff • Thick husk
• Thin kernel

Tenera HhFf • Thick husk
• Thick kernel

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Parental Thin husk and X Thick husk and
phenotype thick kernel thin kernel
Parental genotype
Meiosis hhFF HHff

Gamete Hf Hf Hf Hf

Fertilisation

Genotype F1 HhFf HhFf HhFf HhFf

F1 genotype ratio 4 HhFf
F1 phenotype 100% thick husk and thick kernel
ratio

F1 X F1 Thin husk and X Thin husk and
F1 Phenotype thick kernel thick kernel

F1 Genotype HhFf HhFf
Meiosis
HF Hf hF hf HF Hf hF hf
Gamete

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Punnet squere

Male gamete hF hf
HF Hf HhFF HhFf
HhFf Hhff
HF HHFF HHFf hhFF hhFf
hhFf hhff
Female gamete Hf HHFf HHff

hF HhFF HhFf

hf HhFf Hhff

F2 F2 Phenotype F2 Genotype F2 Phenotype ratio
Genotype ratio 9
1 3
HHFF Thick husk 2 3
HHFf Thick kernel 2
HhFF 4
1
HhFf
2
Hhff Thick husk 1
2
HHff Thin kernel

hhFF Thin husk 11
hhFf Thick kernel

hhff Thin husk
Thin kernel

From the table shows that when Tenera cross with Tenera, it will produce F2
offspring by ratio 9 : 3 : 3 : 1

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11.4 INHERITANCE IN HUMANS

1. Human somatic cell consists two types of chromosomes

Autosomes - Numbers of chromosomes are 44
Sex chromosomes - Vary in size and length
- Numbers of chromosomes are 2

Feature Autosome Sex chromosome
Function
Example Consists of chromosome pairs Consists of one chromosome pair,
from number 1 to 22 that is number 23
Controls all characteristics of Consists of genes which determine
somatic cells gender
Types of blood groups, height and Male has XY chromosomes
skin colour Female has XX chromosomes

2. karyotype is a number and structure of chromosomes present in a cell nucleus
3. Chromosomes are arranged in pairs, based on homologous chromosomes in terms of their

sizes, centromere locations and banding pattern of chromosomes.

Male Karyotype Female Karyotype

Sex chromosome Sex chromosome
Male karyotype (44 + XY) Female karyotype (44 + XX)

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4. Changes in number of chromosomes can occur due to;
Failure of homologous chromosomes to separate during anaphase I
Failure of sister chromatids to separate during anaphase II
Known as nondisjunction

5. Nondisjunction will be causing gametes will have abnormal number of chromosomes
which are 22 or 24

6. Fertilisation between abnormal gamete with a normal gamete produces a zygote with 45
chromosomes or 47 chromosomes

7. Examples of genetic diseases caused by nondisjunction are Down syndrome, Turner
syndrome and Klinefelter syndrome

Genetic diseases Karyotype

Down Syndrome

1. Total chromosome number is 47
2. Which is 45 + XY
3. Has an extra chromosome for

chromosome pair number 21
Also known as trisomy 21

4. Can occur in both males and females.

Turner syndrome

1. Total number of chromosomes is 45
2. Which is 44 + XO.
3. There is a missing X chromosome in the

pair of sex chromosomes
4. Gender of individual with Turner

syndrome is a female.

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Karyotype
Genetic diseases

Klinefelter syndrome

1. Karyotype has a total of 47
chromosomes

2. Which is 44 + XXY
3. Has an extra X chromosome in the pair

of sex chromosomes
4. Gender of individual with Klinefelter

syndrome is male.
5. Secondary sex characteristics are not

well-developed.

HUMAN INHERITANCE

ABO Blood Groups

1. Human ABO blood group is an example of multiple allele
2. Three allele involved which are IA, IB and IO
3. Blood group is controlled by a gene which consists of three different alleles which are allele

IA, IB and IO
4. These alleles determine the types of antigens present on the surface membrane of red

blood cells
5. A person only possesses two alleles to determine they blood group
6. Both IA and IB are dominant alleles whereas IO is recessive allele
7. Combination of IA and IO (IAIO) alleles expresses a group A blood phenotype
8. Combination IBIO expresses a group B blood phenotype
9. IA and IB alleles are codominant and combination of f both alleles give an AB blood group

phenotype

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Genotype Phenotype Type of antigen on Antibodies in blood
(blood erythrocytes plasma
group)

IAIA
A

IAIO

Antigen A Antibody-B

IBIB
B

IBIO

Antigen B Antibody-A

IAIB AB No antibody

Antigen A and B

IOIO O

No antigen Antibody-A and B

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Practice 1:

Blood groups A and B are dominant over blood group O. What is the ratio of their children
blood group phenotype if heterozygous A blood group men marry women with blood group O?

Key : IA Represents dominant alleles for group blood A
IB Represents dominant alleles for group blood B
IO Represents recessive alleles for group blood O

Parental phenotype Male with group Female with group
blood A blood O
Parental genotype
Meiosis IA IO X IO IO
Gamete
Fertilisation IA IO IO IO
Genotype F1
F1 genotype ratio IA IO IA IO IO IO IO IO
F1 phenotype ratio
1 IA IO : 1 IO IO
50% blood A : 50% blood O

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Exercise 2:

Encik Zul has a B blood group while his wife Puan Fifi has A blood group. After blood test,
they found that the daughter blood group is O. By using schematic diagram, explain how this
phenomenon can occur.

Key : IA Represents dominant alleles for group blood A
IB Represents dominant alleles for group blood B
IO Represents recessive alleles for group blood O

Parental phenotype Male with group Female with group
blood A blood B
Parental genotype
Meiosis IA IO X IB IO
Gamete
Fertilisation IA IO IB IO

Genotype F1 IA IB IA IO IB IO IO IO
F1 genotype ratio
F1 phenotype ratio 1 IA IB : 1 IA IO : 1 IB IO : 1 IO IO
1 AB Blood : 1 A blood : 1 B blood : 1 O blood

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1. During meiosis, Encik Zul will produce gametes inherited alleles IB and IO while Puan Fifi
will produce gametes inherited alleles IA and IO

2. During fertilisation, gamete with allele IO from Encik Zul fertilized with gamete with allele
IO from Puan Fifi

3. Produce the offspring with genotype is IOIO
4. Because both alleles are IO, so offspring phenotype for blood group is O

Rhesus Factor (Rh)

1. Surface of human red blood cell also consists antigen D
2. Known as Rhesus factor (Rh)
3. An individual whose red blood cell has Rhesus factor is said to be Rhesus positive (Rh+)
4. An individual without the Rhesus factor is said to be Rhesus negative (Rh–).

Antigen B Antigen B

B+ Antigen D B-

Positive rhesus (Rh+) Negative rhesus (Rh-)

5. Rhesus factor is controlled by genes which Rh+ dominant and Rh– recessive
6. Genotype of a Rh positive individual is either homozygous dominant (Rh+Rh+) or

heterozygous (Rh+Rh–)
7. Rh negative individual is homozygous recessive (Rh–Rh–).

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Exercise 1:

A Rhesus positive is dominant compare to Rhesus negative in human blood. A male with
heterozygous Rhesus married with female with heterozygous Rhesus. What a ratio of
Rhesus in their children?

Key : Rh+ represent dominant allele for Rhesus positive
Rh– represent recessive allele for Rhesus negative

Parent phenotype

Positive rhesus X Positive rhesus
male female
Parent genotype
Meiosis Rh+Rh– Rh+Rh–

Gamete Rh+ Rh– Rh+ Rh–
Fertilisation
Rh+Rh+ Rh+Rh– Rh+Rh– Rh–Rh–
F1 genotype
F1 genotype ratio 1 Rh+Rh+ : 2 Rh+Rh– : 1 Rh–Rh–
F1 phenotype ratio
75% positive rhesus : 25% negative rhesus

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Exercise 2:

Positive rhesus is dominant over negative rhesus. What is the ratio of their offspring's rhesus
phenotype if heterozygous rhesus negative males marry to rhesus positive females?

Key : Rh+ represent dominant allele for Rhesus positive
Rh– represent recessive allele for Rhesus negative

Parent phenotype Negative rhesus X Positive rhesus
male female
Parent genotype
Meiosis Rh–Rh– Rh+Rh–
Gamete
Fertilisation Rh– Rh– Rh+ Rh–
F1 genotype
F1 genotype ratio Rh+Rh– Rh–Rh– Rh+Rh– Rh–Rh–
F1 phenotype ratio
1 Rh+Rh– : 1 Rh–Rh–
50% positive rhesus : 50% negative rhesus

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Thalassemia

1. Thalassemia is an inherited disease
2. Disease can be passed down from generation to generation
3. Caused by gene mutation on an autosome on chromosome 11 or 16
4. Abnormal haemoglobin produced.
5. Size of erythrocytes smaller than normal and the colour of erythrocytes paler.
6. Erythrocytes less efficient in transporting oxygen.
7. The symptom of thalassemia are;

Fatigue Lack of energy Slow growth rate
Anemia Weak Premature birth
Pale Jaundice Swollen liver and spleen

Normal red blood cell Thalassemia red blood cell

8. Person which has heterozygous allele is said thalassemia carrier
Have a thalassemia minor condition
The individual does not show any symptoms of the disease

9. Thalassemia patient is said to have thalassemia major when the individual has both the
recessive alleles

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Exercise 1:

Thalassaemia is genetic disorder carried by recessive autosomal allele. What is their
children’s haemoglobin in blood phenotype ratio when normal haemoglobin male
marries with a thalassaemia carrier female?

Key: R Represent dominant allele for normal haemoglobin
r Represent recessive allele for thalassaemia

Parental phenotype

Normal X Normal haemoglobin
(carrier) female
haemoglobin male
Rr
Parental genotype RR
Meiosis
RR Rr
Gamete
Fertilisation RR Rr RR Rr
F1 genotype
F1 genotype ratio 1 RR : 1 Rr

F1 phenotype ratio 1 1
Normal : Normal haemoglobin
haemoglobin
(carrier)

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Exercise 2:

Thalassaemia is genetic disorder carried by recessive autosomal allele. What is their
children’s haemoglobin in blood phenotype ratio when thalassaemia carrier male
marries with a thalassaemia female?

Key: R Represent dominant allele for normal haemoglobin
r Represent recessive allele for thalassaemia

Parental phenotype

Normal haemoglobin X Normal haemoglobin
(carrier) male (carrier) female
rr
Rr

Parental genotype Rr rr
Meiosis
Rr Rr rr rr
Gamete
Fertilisation 1 Rr : 1 rr
F1 genotype
F1 genotype ratio 50% 50%
Normal haemoglobin : Thalassaemia
F1 phenotype ratio haemoglobin
(carrier)

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Sex Determination

1. A male has 44 + XY chromosomes and a female has 44 + XX
2. Human female ova produced contain 22 autosomes and one X chromosome (22+X)
3. Sperm in male carry two types of chromosomes;

Sperms with 22 autosomes and one X chromosome (22 + X)
Sperms with 22 autosomes and one Y chromosomes (22 + Y).
4. Father’s sperm that determine the sex of the child.
5. Child is female if sperm that carry X chromosome fertilises the ovum
6. Child is male If the sperm carry Y chromosome fertilises the ovum

Parental phenotype

Male X Female
44 + XY 44 + XX
Parental genotype
Meiosis 22 + X 22 + Y 22 + X 22 + X
Gamete
44 +XX 44 + XX 44 + XY 44 + XY
Fertilisation
1 44 + XX : 1 44 + XY
F1 genotype 1 Female : 1 Male
F1 genotype ratio
F1 phenotype ratio

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Jisrun Najaah Fi Ilmi Al Insan Chapter 11: Inheritance

Sex-Linked Inheritance

1. Sex-linked genes located on sex chromosomes
2. Control specific characteristics but are not involved in sex determination
3. Genes of colour blindness and haemophilia are located in the X chromosome
4. Characteristics of colour blindness and haemophilia are caused by recessive genes linked

to X chromosome
5. Y chromosome is shorter than X chromosome

Does not contain as many alleles as X chromosome.
Traits in males caused by either the dominant allele or recessive allele carry by
chromosome X
6. In female, she will inherit this disease when her genotype is homozygous recessive.
7. If her genotype is heterozygous, she is normal because recessive allele for sex-linked
disease is suppress by dominant allele
8. But she may pass the recessive allele to her offspring.
9. These heterozygous females are called carrier.
10. While in male, he will suffer the disease when inherit recessive allele from his mother
11. Because male possess only one X chromosome.
12. This the main reason why more males is suffer sex-linked

Genotype Phenotype
XHXH • Normal female
XHXh • Carrier female
XhXh • Disease’s female
YXH • Normal male
YXh • Disease’s male

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Colour Blindness
1. Condition in which a person cannot differentiate some specific colours such as red and

green
2. Caused by the recessive allele found in the X chromosome
3. Most people with colour blindness are males.

Colour blindness is genetic disorder carried by X recessive allele. What is their children
colour eyesight phenotype ratio when normal colour eyesight male married with carrier
female?

Key : XB Represent dominant allele for normal colour eyesight.

Xb Represent recessive allele for colour blindness.

Parental
phenotype

Parental Normal colour Normal colour eyesight
genotype eyesight male X (carrier) Female
Meiosis
XBY XBXb
Gamete
Fertilisation XB Y XB Xb

F1 genotype XB XB X B Xb XBY XbY

F1 genotype 1 XB XB : 1 XB Xb : 1 XBY : 1 XbY
ratio
11
F1 phenotype 11
ratio Normal colour colour
Normal colour : : Normal colour :
eyesight blind male
eyesight female eyesight male
(carrier) female

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Jisrun Najaah Fi Ilmi Al Insan Chapter 11: Inheritance

Exercise 1:

Colour blind is genetic disorder carried by X recessive allele. What is their children
colour eyesight phenotype ratio when colour blinded male married with carrier colour
blindness female?

Key: XB Represent dominant allele for normal colour eyesight.
Xb Represent recessive allele for colour blindness.

Parental Colour blind Normal colour eyesight
phenotype male X (carrier) Female

Parental Xb Y XBXb
genotype
Meiosis Xb Y XB Xb

Gamete
Fertilisation

F1 genotype XBXb XbXb XBY XbY

F1 genotype 1 XBXb : XbXb : XBY : 1 XbY
ratio
1 : 1 1
F1 phenotype Normal colour Colour blind 1
ratio eyesight female
female colour
(carrier) : Normal colour :

blind male
eyesight male

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Jisrun Najaah Fi Ilmi Al Insan Chapter 11: Inheritance

Haemophilia

1. Condition in which blood cannot clot in normal circumstances
2. Caused by lack of blood clotting factor VIII in platelet

Due to the presence of the recessive allele in the X chromosome
3. Result in excessive internal or external bleeding which may be fatal

Haemophilia is genetic disorder carried by X recessive allele. What are their children
blood clotting phenotype ratio when normal male married with carrier female?

Key: XH Represent dominant allele for normal blood clotting
Xh Represent recessive allele for haemophilia

Parental Normal blood X Normal blood clot
phenotype clot male (carrier) Female

Parental XH Y XHXh
genotype
Meiosis XH Y XH Xh

Gamete
Fertilisation

F1 genotype XHXH XHXh XHY XhY

F1 genotype 1 XHXH : 1 XHXh : 1 XHY : 1 XhY
ratio
1 1 1 1
F1 phenotype Normal Normal blood Normal Haemophilia
ratio blood clot :: blood clot :
female clot (carrier)
male male
female

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Jisrun Najaah Fi Ilmi Al Insan Chapter 11: Inheritance

Exercise 1:

Haemophilia is genetic disorder carried by X recessive allele. What is their children blood
clotting phenotype ratio when normal male married with haemophilia female?

Key: XH Represent dominant allele for normal blood clotting
Xh Represent recessive allele for haemophilia

Parental phenotype

Normal blood X Haemophilia
clot male female
Parental genotype
Meiosis XH Y XhXh

Gamete XH Y Xh Xh
Fertilisation
XHXh XHXh XhY XhY
F1 genotype 1 XhY
F1 genotype ratio 1 XHXh :

F1 phenotype ratio 11

Normal blood clot : Haemophilia

(carrier) female male

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Jisrun Najaah Fi Ilmi Al Insan Chapter 11: Inheritance

Ability to Roll Tongue

Roll Tongue is characteristics that can be inherited from parents to children. What is their
children ability to roll tongue phenotype ratio when heterozygous male can roll tongue married
with female can’t roll tongue?

Key: R Represent dominant allele for can roll tongue
r Represent recessive allele for can’t roll tongue

Parental phenotype Can roll Can’t roll
tongue male X tongue female
Parental genotype
Meiosis Rr rr
Gamete
Fertilisation Rr rr
F1 genotype
F1 genotype ratio Rr Rr rr rr
F1 phenotype ratio
1 Rr : 1 rr

50% 50%
can roll tongue :

can’t roll tongue

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Jisrun Najaah Fi Ilmi Al Insan Chapter 11: Inheritance

Types of Earlobes

Types of Earlobes is characteristics that can be inherited from parents to children. What are
their children’s types of earlobe phenotype ratio when heterozygous male free earlobe married
with female attached earlobe?

Key: F Represent dominant allele for free earlobe
f Represent recessive allele for attached earlobe

Parental phenotype Free earlobe Attached
male X earlobe female
Parental genotype
Meiosis Ff ff
Gamete
Fertilisation Ff f
F1 genotype
F1 genotype ratio Ff ff
F1 phenotype ratio 1 Ff : 1 rr

1 1
Free earlobe :

Attached earlobe

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Jisrun Najaah Fi Ilmi Al Insan Chapter 11: Inheritance

Family Pedigree

1. Flowchart to investigate inheritance of human characteristics
2. To analysis ancestral relationship and inheritance of characteristics from ancestors to

individuals in the present generation
3. Enables the geneticist to predict an inherited characteristic of interest and also to identify

the features of dominant or recessive gene
4. Dominant gene appears in every generation
5. Recessive gene is probably hidden in certain generations

Parent in each generation

Each generation I 12
is symbolised by II Marriage
a Roman numeral
and is placed on 1 2 34 5
the left

Children

III 1 2 3 4 123 4

Symbols used in Children Children
pedigree 213

Normal male
Normal female
Haemophilic male
Haemophilic female
Female carrier

Jisrun Najaah Fi Ilmi Al Insan Chapter 11: Inheritance

Exercise 1:
Encik Ali married with Puan Aina and they have three children which are Abu, Isa and Mila.
They son Abu, married with Leha and have four children which are Ana, Elsa, Olaf and Sven.
Based on the pedigree below complete the diagram. Determine the phenotype and genotype
of Abu, Puan Aina and Leha.

Symbols used in
pedigree

Puan Aina En. Ali Normal male
Normal female

Mila Isa Abu Leha Colour blind male
Colour blind female

Female carrier

Ana Elsa Olaf Sven

Key: XB Represent dominant allele for normal colour eyesight.
Xb Represent recessive allele for colour blindness.

Name Phenotype Genotype
Puan Aina Carrier colour blind XBXb
Abu Colour blind male XbY
Leha Normal female XBXB

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