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CHAPTER 4: GENETIC INHERITANCE

SUBTOPIC: 4.1 Mendelian genetics: Monohybrid and Dihybrid

LEARNING OUTCOMES:

a) Define the terminologies used in genetic inheritance: allele, gene, locus, genotype, phenotype, homozygous, heterozygous, dominant, recessive, self-cross and test cross.

b) State the characteristics of Mendel’s pea plants. c) State Mendel’s first law (Law of Segregation). d) Construct genetic diagram on the monohybrid cross and include the genotypic ratio

(1:2:1) and phenotypic ratio (3:1) of F2 generation.

e) Construct genetic diagram on Mendelian monohybrid test cross and include the genotypic ratio (1:1) and phenotypic ratio (1:1).

f) State Mendel’s second law (Law of Independent Assortment). g) Construct genetic diagram on the dihybrid cross and include only phenotypic ratio

(9:3:3:1) of F2 generation using Punnett square.

h) Construct genetic diagram on Mendelian dihybrid test cross and include phenotypic ratio (1:1:1:1) of F2 generation using Punnett square.

1. Match the vocabulary word with the proper definition.

Vocabulary Definition

1 Allele involves the breeding of an individual with a

phenotypically recessive individual,

2 Gene masks the recessive allele; an organism with a

dominant allele will exhibit that form of the trait;

represented by a capital letter

3 Locus the genetic constitution of a individual; genetic

makeup

4 Genotype sequence of DNA that codes for a protein and

determines a trait

5 phenotype term used to refer to an organism that has two

different alleles for the same trait

6 homozygous any location on a chromosome, or any region of

genomic DNA

7 heterozygous term used to refer to an organism that has two

identical alleles for a particular trait

8 Dominant A cross between male and female from the same

plants/generation

9 Recessive describes the total physical appearance of an

organism; physical characteristics

10 Self pollination

one of a number of different forms of a gene

11 Test cross masked by the dominant allele; organisms will only

exhibit this form of the trait if the dominant allele is

not present; represented by a lower case letter

BIOLOGY TUTORIALWORKSHEET

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2. Mendel chose pea plants (Pisum sativum) because they possess four important qualities. These

qualities are:

(a) All offspring will have the same _____ characteristics generation after generation.

(b) Peas have contrasting traits. (eg. purple vs. white flowers)

(c) Peas usually reproduce by _____________ pollination because of its anatomy.

(d) Pea plants grow quickly and do not require much space.

3. The seven contrasting traits that Mendel observed in Pisum sativum are:

(a) Pea shape (R) - _________________ or __________________

(b) Pea color (Y) – yellow or green

(c) Pod shape (I) – inflated or constricted

(d) Pod color (G) – green or yellow

(e) Flower color (P) - _________________ or __________________

(f) Plant size (T) – tall or dwarf

(g) Position of flowers (A) – axial or terminal

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4. Multiple Choice: Circle the letter of the correct choice.

Mendel’s First Set of Experiments

At first, Mendel experimented with just one characteristic at a time. He began with flower colour. As

shown in the figure below, Mendel cross-pollinated purple- and white-flowered parent plants. The parent

plants in the experiments are referred to as the P (for parent) generation.

This diagram shows Mendel’s first experiment with pea plants. The F1 generation results from cross-

pollination of two parent (P) plants. The F2 generation results from self-pollination of F1 plants.

F1 and F2 Generations

The offspring of the P generation are called the F1 (for filial, or “offspring”) generation. As you can see

from the figure above, all of the plants in the F1 generation had purple flowers. None of them had white

flowers. Mendel wondered what had happened to the white-flower characteristic. He assumed some type

of inherited factor produces white flowers and some other inherited factor produces purple flowers. Did

the white-flower factor just disappear in the F1 generation? If so, then the offspring of the F1 generation

— called the F2 generation — should all have purple flowers like their parents.

To test this prediction, Mendel allowed the F1 generation plants to self-pollinate. He was surprised by the

results. Some of the F2 generation plants had white flowers. He studied hundreds of F2 generation plants,

and for every three purple-flowered plants, there was an average of one white-flowered plant.

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Law of Segregation

Mendel did the same experiment for all seven characteristics. In each case, one value of the characteristic

disappeared in the F1 plants and then showed up again in the F2 plants. And in each case, 75 percent of F2

plants had one value of the characteristic and 25 percent had the other value. Based on these observations,

Mendel formulated his first law of inheritance. This law is called the law of segregation. It states that

there are two factors controlling a given characteristic, one of which dominates the other, and these

factors separate and go to different gametes when a parent reproduces.

1. Why did Mendel choose to work with the garden pea plant? A. Because the pea plant is easy to work with. B. Because pea plants are fast growing. C. Because the pea plant has a number of characteristics, each with only two forms. D. All of the above

2. In Mendel's first experiment A. the F1 displayed all purple-flowered plants. B. the F1 displayed all white-flowered plants. C. the F2 displayed all purple-flowered plants. D. the F2 displayed half purple-flowered and half white-flowered plants.

3. The law of independent assortment states that A. two factors of the same characteristic separate into different gametes. B. there are dominant and recessive factors. C. factors controlling different characteristics are inherited independently of each

other.

D. there are two factors that control inheritance.

4. Looking at your cat will give information concerning A. the cat's genotype. B. the cat's phenotype. C. the cat's recessive alleles. D. the cat's heterozygous alleles.

5. Which sentence is correct?

A. Different alleles of the same gene are located at the same locus on different homologous chromosomes.

B. Different alleles of the same gene are located at different loci on different homologous chromosomes.

C. Different genes of the same alleles are located at the same locus on different homologous chromosomes.

D. Different alleles of the same gene are located at different loci on the same chromosome.

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6. An Aa individual

A. has a homozygous genotype. B. has a heterozygous phenotype. C. has a heterozygous genotype. D. has a homozygous phenotype.

7. In Mendel's initial experiments, an example of the F2 generation would be

A. 75 round seed plants to 25 wrinkled seed plants B. 75 green seed plants to 25 yellow seed plants C. 75 white-flowered plants to 25 purple-flowered plants D. all of the above

8. Which of the following is part of the law of segregation?

(1) there are two factors controlling a given characteristic,

(2) one factor is dominant over the other factor,

(3) the two factors separate into different gametes.

A. 1 and 2 B. 1 and 3 C. 2 and 3 D. 1, 2, and 3

5. Set up the Punnett squares for each of the crosses listed below. Round seeds are dominant to

wrinkled seeds.

(a) RR x rr

What percentage of the offspring will be round?

(b) Rr x rr

What percent of the offspring will be round?

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(c) RR x Rr

What percent of the offspring will be round?

(d) Rr x Rr

What percent of the offspring will be round?

(e) From (a), (b), (c), and (d), which one produces genotypic ratio (1:2:1) and phenotypic

ratio (3:1)?

6. A male and female bird has 4 un-hatched eggs. The female on the left is heterozygous; the male

on the right is homozygous recessive. Use G or g for your genotypes.

(a) Write the genotype of the female (left): _________________________________

(b) Write the genotype of the male (right): __________________________________

(c) Which colour is dominant, gray or black? How do you know?

___________________________________________________________________

___________________________________________________________________

(d) Write the phenotype of the female and the phenotype of the male below:

___________________________________________________________________

___________________________________________________________________

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(e) Complete the Punnett square below for this couple:

(f) What is the predicted genotypic ratio of the offspring?

___________________________________________________________________

(g) What will be the colour of the baby birds?

___________________________________________________________________

7. Dihybrid crosses examine two unlinked (on different chromosomes) gene loci. The following

problem uses many of the skills you learned in the section on monohybrid crosses.

In peas, a single gene codes for stem length and another single gene codes for seed shape. Each

gene has two alleles, one dominant and one recessive. For stem length, tall plants are dominant

over short plants. For seed shape, smooth peas are dominant over wrinkled peas.

A. Choose letters to represent each gene and its alleles.

Seed shape: Smooth:_____ wrinkled:_____

Stem length: Tall:______ short:______

B. In Table 4.1 is a list of all the possible phenotypes for this pair of traits. Determine the

genotypes for these plants, in some cases there will be multiple possible genotypes. When we

worked with one gene locus, each individual genotype was represented by 2 letters since

individual organisms are diploid. Now we are working with two gene loci, so each individual

genotype will be represented by 4 letters, 2 letters for each gene locus. The first genotype is

given.

C. For each of the individuals in part B, list all the unique gametes that can be produced.

Remember, each gamete will have 1 allele from each gene locus. When we worked with a single

gene, each gamete genotype was represented by 1 letter. Now we are working with 2 gene loci, so

each gamete genotype will be represented by 2 letters, one from each gene locus. Fill in the rest

of the Table with all the possible gamete genotypes for each parent genotype listed. The first

gamete genotype is given.

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TABLE 4.1 Table of Genotypes for Two Loci

Phenotype Possible genotype Possible gametes

SMOOTH, TALL SSTT ST

wrinkle, TALL

SMOOTH, short

wrinkle, short

(a) Determine the F1 genotypes and phenotypes resulting from a cross of a homozygous smooth and

homozygous tall plant with a wrinkled, short plant.

(b) What are the F2 genotypes and phenotypes (crossing two F1 )

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8. In pea plants, green pod colour is dominant over yellow pod colour. Tall plant height is dominant

over short plant height.

(a) A tall green pea plant (TTGG) is crossed with a short white pea plant (ttgg).

TT or Tt = tall tt = short GG or Gg = green gg = white

Parental Generation genotypes: ___________ x ___________

Possible gametes: ___________________________________

Phenotypic Ratio: ___ tall/green : ___ tall/yellow : ___ short/green : ___short/ yellow

Genotypic Ratio: _______________________________________________________

(b) A tall green pea plant (TtGg) is crossed with a Short white pea plant (ttgg).

Parental Generation genotypes: ___________ x ___________

Possible gametes: ___________________________________

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Phenotypic Ratio: ___ tall/green : ___ tall/yellow : ___ short/green : ___short/ yellow

Genotypic Ratio: _______________________________________________________

(c) Two heterozygous tall, green pea plants are crossed.

Parental Generation genotypes: ___________ x ___________

Possible gametes: ___________________________________

Phenotypic Ratio: ___ tall/green : ___ tall/yellow : ___ short/green : ___short/ yellow

Genotypic Ratio: _______________________________________________________

9. Set up a Punnett square using the following information:

Dominant allele for black fur in guinea pigs = B

Recessive allele for white fur in guinea pigs =b

Dominant allele for rough fur in guinea pigs =R

Recessive allele for smooth fur in guinea pigs = r

Cross a heterozygous parent (BbRr) with a heterozygous parent (BbRr).

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a. What is the probability of producing guinea pigs with black, rough fur? Possible genotype(s)?

b. What is the probability of producing guinea pigs with black, smooth fur? Possible genotype(s)?

c. What is the probability of producing guinea pigs with white, rough fur? Possible genotype(s)?

d. What is the probability of producing guinea pigs with white, smooth fur? Possible genotype(s)?

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SUBTOPIC: 4.2 Deviations from the Mendelian inheritance

LEARNING OUTCOMES:

a) Explain briefly types of inheritance that deviate from Mendelian: Codominant alleles,

incomplete dominant alleles, multiple alleles, linked genes, sex-linked genes and polygenes.

Complete table below:

Description Types of inheritance that

deviate from Mendelian

Examples

Both alleles of a pair are fully

expressed in a heterozygote

Codominant alleles

Incomplete dominant

alleles

Colour of snapdragon flower

Antirrhinum majus

More than two alleles control

for particular trait of a

character

Multiple alleles

Linked genes

Genes that are carried by

either sex chromosomes (X

and Y)

Sex-linked genes

Polygenes

Skin colour

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Codominant alleles

1. The alleles governing the MN blood group system in man are codominant and

may be represented by the symbols LM and LN.

Genotype Blood group (phenotype)

LMLM M

LMLN MN

LNLN N

Use the genetic diagram to show the expected phenotypic ratio for the crosses

between two heterozygous individuals.

2. Human blood types are determined by genes that follow the CODOMINANT pattern of

inheritance. There are two dominant alleles (IA and IB) and one recessive allele (i).

Blood Type

(Phenotype)

Genotype Can donate blood to: Can receive blood from:

O

ii

A,B,AB and O

(universal donor)

O

AB

IAIB

AB

A,B,AB and O

(universal receiver)

A

IAIA or IAi

AB, A

O,A

B

IBIB or IAi

AB,B

O,B

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(a) Write the genotype for each person based on the description:

a. Homozygous for the “B” allele : _______________________________________

b. Heterozygous for the “A” allele : _______________________________________

c. Type O : __________________________________________________________

d. Type “A” and had a type “O” parent : ___________________________________

e. Type “AB” : _______________________________________________________

f. Blood can be donated to anybody : _____________________________________

g. Can only get blood from a type “O” donor : ______________________________

(b) Pretend that Brad Pitt is homozygous for the type B allele, and Angelina Jolie is type

“O.” What are all the possible blood types of their baby?

(c) Draw a Punnett square showing all the possible blood types for the offspring produced by

a type “O” mother and an a Type “AB” father.

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Incomplete dominant alleles

1. Snapdragon are incomplete dominant for colour, they have phenotypes red, pink and

white. The red and white flowers are homozygous, and the pink flowers are

heterozygous. Give the genotypes for each of the phenotypes, using the letters “R” and

“W” for alleles:

a. Red snapdragon : ___________________________________________________

b. Pink snapdragon : ___________________________________________________

c. White snapdragon :__________________________________________________

2. Show genetic crosses between the following snapdragon parents, using the punnett

squares provided, and record the genotypic and phenotypic ratios below:

a. Pink x Pink

% Red snapdragon : _____________________________

% Pink snapdragon : _____________________________

% White snapdragon : ___________________________

Genotypic ratio : ________________________________

Phenotypic ratio: _______________________________

b. Red x White

% Red snapdragon : _____________________________

% Pink snapdragon : _____________________________

% White snapdragon :___________________________

Genotypic ratio : ________________________________

Phenotypic ratio: _______________________________

gametes

gametes

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c. Pink x White

% Red snapdragon : _____________________________

% Pink snapdragon : _____________________________

% White snapdragon : ___________________________

Genotypic ratio : ________________________________

Phenotypic ratio: _______________________________

3. The shapes and colours in carrots are determined by two pairs of different alleles. Both

pairs of alleles did not show dominancy. Each genotype produces different phenotypes.

Colours of carrots are red (CRCR), purple (CRCW) or white (CWCW). The shapes are long

(SLSL), oval (SLSN) or round (SNSN).

(a) What type of inheritance is shown by the shape and colours of carrot? [1 mark]

__________________________________________________________________

(b) The long, red carrot is crossed with the round, white carrot. With a genetic

diagram, show the parent genotypes, gametes and F1 generation. [3 marks]

gametes

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(c) If the F1 generation is self-crossed, what are the frequencies for the following

phenotypes? [4 marks]

Phenotypes Frequency

Red, oval

Purple, long

White, long

White, round

(d) If the purple, oval carrot has the highest demand in the market, give TWO

possible crosses that can be done to meet the demand. [2 marks]

__________________________________________________________________

__________________________________________________________________

4. With the aid of genetic diagram, explain incomplete dominance and its inheritance in

snapdragon (Antirrhinum sp.) [12 marks]

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Multiple alleles

1. Human blood types are determined by genes with multiple alleles. Each person can have

two of the four possible alleles. These alleles will specify if there is a type of molecule on

the surface of blood cells (A, B, AB) or none (O).

Blood type

(Phenotype)

Genotype Can donate blood to Can receive blood from

O ii A, B, AB and O

(Universal donor)

O

AB IAIB AB A, B, AB and O

(Universal receiver)

A IAIA

IAi

AB, A O, A

B IBIB

IBi

AB, B O, B

(a) Draw a Punnett square showing all the possible blood types for the offspring produced by

a type “O” mother and an a type “AB” father. Draw genetic diagram and record the

genotypic and phenotypic ratios

P phenotype :

P genotype :

Gamete :

F1 generation :

Genotypic ratio :

Phenotypic ratio :

gametes

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(b). Two parents think their baby switched at the hospital. It’s 1968, so DNA fingerprinting

technology does not exist yet. The mother has blood type “O”, the father has blood type

“AB” and the baby has blood type “B”.

a. Mother’s genotype :_______________________________________________

b. Father’s genotype :_______________________________________________

c. Baby’s genotype :_______________________________________________

d. Punnett square showing all possible genotypes for children produced by this

couple:

e. Draw genetic diagram for the above cross.

P phenotype :

P genotype :

Gamete :

F1 generation :

Genotypic ratio :

Phenotypic ratio :

f. Was the baby switched?

__________________________________________________________________

gametes

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2. The ABO blood group system in human is an example of interactions of alleles that

are illustrated by multiple alleles.

(a) What is meant by multiple alleles? [2 marks]

____________________________________________________________________

____________________________________________________________________

(b) State the alleles that control the ABO blood group system in humans. [1 mark]

____________________________________________________________________

(c) State the likely allele combinations in ABO blood group system. [3 marks]

____________________________________________________________________

____________________________________________________________________

(d) The table below shows three husband and wife couples with their respective blood

groups and their percentage of the number of children produced in accordance with

blood groups. State the parents’ genotype for each of the crossed couples in the table

below. [3 marks]

Couple Parents’

blood

Percentage of number of

children in accordance with

blood group

Parents’ genotype

A

B AB O

First O X A 50 - - 50

Second B X A 25 25 25 25

Third A X AB 50 25 25 -

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Linked genes

1. In pea, the gene for green seed (G), and smooth seed (S), are dominant over the

genes for yellow seed and wrinkled seed. Pure breeding strains of the dominant and

recessive varieties were crossed. A test cross of the F1 generation produced the following

results:

Green seed, smooth seed 180

Yellow seed, wrinkled seed 193

Green seed, wrinkled seed 7

Yellow seed, smooth seed 6

(a) (i) Does the above cross follow the Mendelian ratio? [1 mark]

__________________________________________________________________

(ii) Explain how the situation in (a)(i) occurs. [2 marks]

__________________________________________________________________

__________________________________________________________________

(b) Draw the genetic diagram for the test cross of F1 generation. [4 marks]

(c) Calculate the distance between the two genes. Show your calculation. [3 marks]

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3. Black coloured body and vestigial wings in Drosphila sp. are controlled by two recessive

alleles b and vg. Dominant alleles, b+ and vg+ produce wild type (grey coloured body

and normal wings). A homozygous wild type is crossed to a homozygous black coloured

body and vestigial wings. The F1 progenies produced are all of wild type and are crossed

with homozygous recessive. The F2 generations are as follows:

442 wild type : 458 black, vestigial : 46 black, normal : 54 grey,vestigial

(a) Using genetic diagram, explain the results shown above. [6 marks]

(b) Calculate the distance between the genes controlling the body colour and the type of

wing. [2 marks]

(c) If the genes are not linked, what is the expected number of individuals of each

phenotype in the F2 generation? [2 marks]

_____________________________________________________________________

_____________________________________________________________________

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Sex-linked genes

1. In fruit flies, eye color is a sex linked trait. Red is dominant to white.

(a) What are the sexes and eye colors of flies with the following genotypes:

X R X r _______________ X R Y _______________

X R X R _______________ X r Y _______________

(b) What are the genotypes of these flies:

white eyed, male ______________ red eyed female (heterozygous) _______________

white eyed, female ______________ red eyed, male _______________

(c) Show the cross of a white eyed female X r X r with a red-eyed male X R

Y .

(d) Show a cross between a pure red eyed female and a white eyed male.

i) What are the genotypes of the parents:

__________________________________________________________________

ii) How many are:

white eyed, male _______________

white eyed, female _______________

red eyed, male _______________

red eyed, female _______________

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(e) Show the cross of a red eyed female (heterozygous) and a red eyed male.

i) What are the genotypes of the parents?

__________________________________________________________________

ii) How many are:

white eyed, male_______________

white eyed, female _______________

iii) What if in the above cross, 100 males were produced and 200 females. How

many total red-eyed flies would there be?

red eyed, male _______________

red eyed, female _______________

2. In humans, hemophilia is a sex linked trait. Females can be normal, carriers, or have the

disease. Males will either have the disease or not (but they won’t ever be carriers)

= female, normal

= female, carrier

= female, hemophiliac

= male, normal

= male, hemophiliac

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(a) Show the cross of a man who has hemophilia with a woman who is a carrier. What is the

probability that their children will have the disease?

(b) A woman who is a carrier marries a normal man. Show the cross. What is the

probability that their children will have hemophilia? What sex will a child in the

family with Hemophilia be?

(c) A woman who has hemophilia marries a normal man. How many of their children will have

hemophilia, and what is their sex?

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SUBTOPIC: 4.3 Genetic mapping.

LEARNING OUTCOMES:

a) Define genetic mapping.

b) Calculate the genetic distance (map unit) between genes using the given recombinant

data.

c) Identify the position or order of genes along a chromosome based on recombinant

data.

1. FIGURE 3 shows a testcross.

FIGURE 3

(a) What is the purpose of a testcross? [1 mark]

_______________________________________________________________________

(b) State the Mendel's second law. [1 mark]

________________________________________________________________________

(c) Give the genotypes of:

i) The two parents of P. [2 marks]

__________________________________________________________________

ii) Use Punnett square to show the progenies of the above testcross. [3 marks]

(d) How do recombinant genotypes formed? [1 mark]

_____________________________________________________________________

(e) Assume that a total of 600 progenies are produced, and the map distance between A and D is 18 cM, calculate the most ideal number of each recombinant progeny.

[2 marks]

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2. The following chart shows the crossover frequencies for some genes on an autosome of

organism Z. Construct a chromosome map.

Genes Crossover Frequency

P & Q 5%

P & R 8%

P & S 12%

Q & R 13%

Q & S 17%

3. For a series of experiments, a linkage group composed of genes W, X, Y and Z was found to

show the following gene combinations. (All recombinations are expressed per 100 fertilized

eggs). Construct a gene map.

Genes W X Y Z

W – 5 7 8

X 5 – 2 3

Y 7 2 – 1

Z 8 3 1 –

4. In Drosophila, the gene for eye color (A), wing shape (B), and body color (C) are all found

on the same chromosome. The following crossover frequencies for these genes were

determined by experiments.

Genes Crossover Frequency

A & B 12.5%

A & C 6.0%

B & C 18.5%

What is the correct sequence of the genes A, B and C on the chromosome?

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Multiple Choice Questions

1. Mendel crossed pure breeding plants having smooth seeds with pure breeding plants

having wrinkled seeds. The F1 plants had smooth seeds. Then the F1 plants were

allowed to self-fertilize. Mendel collected 600 F2 plants. How many of these would be

expected to have smooth seeds and how many wrinkled seeds?

A. 400 smooth seeds and 200 wrinkled seeds

B. 300 smooth seeds and 300 wrinkled seeds

C. 450 smooth seeds and 150 wrinkled seeds

D. 150 smooth seeds and 450 wrinkled seeds

2. A genetic cross between an individual showing a dominant phenotype (unknown

genotype) and a homozygous recessive individual is known as a_________________

A. back cross

B. reciprocal cross

C. self-cross

D. test cross

3. A genetic cross of monohybrid plants results in a phenotypic ratio of 1:2:1 in F2

generation demonstrates __________________

A. incomplete dominance

B. multiple allele

C. polygenes

D. linked genes

4. A genetic cross of two plants results in offspring with 9:3:3:1 ratio for a particular trait.

This condition shows ______________

A. the genes controlling the traits were located on same chromosome

B. multiple allele

C. that both parents were heterozygous

D. monohybrid cross

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5. How many unique gametes could be produced through independent assortment by an

individual with the genotype RrSsTTUu?

A. 4

B. 8

C. 16

D. 32

6. A pointed contour off the hairline on the forehead or known as widow’s peak is

dominant to straight hairline in human. A woman with widow’s peak married a man

with straight hairline. They had a daughter with widow’s peak which later also married

to a man with straight hairline. What is the percentage of their first child having widow’s

peak?

A. 100%

B. 70%

C. 50%

D. 25%

7. In fowl, the allele for black feather is incomplete dominant to white feather and

heterozygous is bluish-grey in phenotype or known as Andalusian blue. The second

locus controls the texture of the feathers, in which silky feathers is recessive to normal

feathers. Self-crossed were done on Andalusian blue bird with silky feathers. Predict the

phenotype ratio of the offspring.

A. 1 black, silky : 2 blue,silky : 1 white, silky

B. 1 black, normal : 2 blue, normal : 1white, normal

C. 3 black,silky : 1 white,silky

D. 3 black, normal : 1 white, normal

8. A cross between two true-breeding pea plants were done in which one parent has purple,

axial flowers and other has white, terminal flowers. All the F1 progenies have purple,

axial flowers. The F1 progenies were self-crossed and produced 1500 F2 offsprings.

Approximately how many of them would you expect to have white flowers with axial

position?

A. 90

B. 280

C. 560

D. 850

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9. Phenylketonuria is an inherited disease in human caused by recessive mutant allele. A

man with blood type O married a women with blood type AB, where both are

heterozygous for phenylketonuria inheritance. Predict the probability that their child

having blood type B inherited the disease.

A. 1/8

B. 2/8

C. 3/8

D. 6/8

10. Red-green colour blindness is an X-linked recessive disorder in humans. A boy with

colour blindness inherited the mutant gene from one of his grandfathers. From whom

does he inherit the mutant genes?

A. Maternal grandfather

B. Paternal grandfather

C. Maternal grandmother

D. None of the above

11. Pea plants are chosen by Mendel as the model crop in his breeding experiment because of

_________________

I. Variations in the characteristics found in pea plants are obvious and easily

distinguishable

II. Controlled pollinations that are easy to conduct

III. Produce many healthy offspring

IV. Short life-cycle enables data collection from several generations

A. I, II and III

B. I and III only

C. II and IV only

D. All of the above

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12. Select the correct matching of dominant and recessive traits in pea plants.

Dominant Recessive

I Smooth seeds Wrinkled seeds

II Inflated pods Constricted pods

III Yellow cotyledons Green cotyledons

IV Terminal flowers Axial flowers

A. I, II and III

B. I and III only

C. II and IV only

D. All of the above

13. In Drosophila sp., ebony body colour and vestigial wings are recessive to the wild type

and are not linked. A cross between two flies, heterozygous for both characteristics,

produced 278 offspring. How many offspring would be expected to have normal body

colour and vestigial wings?

A. 18

B. 52

C. 96

D. 157

14. Albinism is caused by a recessive autosomal allele. A normal man who marries a normal

woman have an albino child. What is the genotype of the albino child?

A. Homozygous dominant

B. Homozygous recessive

C. Heterozygous

D. Unknown

15. A man who carries an X-linked allele will pass it on to

A. all of his daughters

B. half of his daughters

C. all of his sons

D. half of his sons

KMPk SB015

32

16. Which one of the following is/are examples of continuous variation in human?

I. Height

II. Skin colour

III. ABO blood system

A. I only

B. I and II only

C. II and III only

D. I, II and III

17. A woman who is carrier of haemophilia and has normal parents, marries a healthy man.

Which one of the following statements is true?

A. her father is carrier of haemophilia

B. her mother is also carrier of haemophilia

C. all of her sons will be haemophiliacs

D. all of her daughters will carry the recessive gene

18. In genetics, map units refer to the distance between

A. homologous chromosome

B. two loci on a chromosome

C. two contrasting alleles

D. kinetochores

19. A blood group A man marries a blood group A woman. What is the probability that their

children will be of blood group O?

A. 12.5%

B. 25%

C. 50%

D. 75%

20. In a two-point test cross, 24 of the offspring were recombinant types. The remaining 76

offspring were parental types. What is the distance of the two loci?

A. 24

B. 36

C. 48

D. 76