Question

Genetics - Worksheet #9 Sex-linkage Problems

Name ____________________________________ Date __________ Class_____

Make sure that you show the crosses for each problem. Make sure you include a key telling what letters you are using for example: H is normal and h is hemophiliac. Remember this is sex- linked so you must show sex chromosomes. Use the foil method.

1. Color blindness in humans is sex-linked and recessive. A normal man marries a woman whose father was colorblind but she was not.  

Cross:

Show the genotypes:

the man

his wife,

the genotypes and phenotypes of their offspring.

2. A man with normal vision marries a woman who also has normal vision. One of their children is      

     colorblind.  

    

   Cross:

Genotypes of the man

Genotype of woman ,  

genotype of their child.

3. Hemophilia is caused by a recessive gene on the X chromosome.  

    A woman whose father was a hemophiliac but who is not one herself marries a normal man.  

Cross:

What are their genotypes and what are the possible genotypes and phenotypes of their children? What percentage of their daughters could be expected to be hemophiliac:

expected to be carriers;

what percentage of their sons will be

hemophiliac: carriers?

4. In cats, certain colors are sex linked. These genes also display incomplete dominance. Use Y for     

      yellow and B for black. Tortoise shell color (Calico) is the combination of both Y and B.  

Cross a tortoise shell female with a black male.

Coss:

Genotypes of offspring:

Phenotypes possible for their offspring.

Why are tortoise shell cats always female?

5. In fruit flies, straight wings is dominant over curved wings. A certain male was mated to a female with curved wings. They produce 50% straight and 50% curved-winged offspring.  

What are the genotypes for the male,

                                        the female

                              and their offspring.

Answer 1

Ans:

1. If her father is color blind, the woman is a carrier for color blind. If a normal male is crossed with carrier female, one normal female, one normal male, one carrier female and one color blind male are produced.

The genotype of husband is XCY

The genotype of wife is XCXc

Genotypes of the child-

Normal female: XCXC

Carrier female: XCXc

Normal male: XCY

color blind male: XcY

The cross is given below-

2.  If a normal vision male is crossed with normal vision female and produce one color blind child, then

The genotype of female is XCXc (carrier female with normal vision) because color blindness is a X-linked recessive disease.

The genotype of male is XCY (Normal vission).

Phenotypes and genotypes of the offsprings -

Normal female: XCXC

Carrier female: XCXc

Normal male: XCY

color blind male: XcY

The cross is given below-

3.

If her father is haemophilia, the woman is a carrier for haemophilia. If a normal male is crossed with carrier female, one normal female, one normal male, one carrier female and one haemophilic male are produced.

Phenotypes and genotypes of the child-

Normal female: XHXH

Carrier female: XHXh

Normal male: XHY

Haemophilic male: XhY

0% of daughters are expected to haemophilic.

50% of daughters are carrier of haemophilic.

0% of sons are carrier of haemophilic

The cross is given below-

4. If a tortoiseshell female cat is crossed with black male, one tortoiseshell female, one yellow male, one black female and one black male cat are produced.

The cross is given below-

The tortoiseshell cat always female because it is a X-linked recessive character and male have only one X chromosome. Due to incomplete dominance, one X chromosome with Y and B allele produces either yellow or black male. Tortoiseshell color is developed if two X chromosomes are present with Y allele in one X chromosome and B in other.

5. If a cross between male and female produces 50% straight and 50% curved offsprings, then

The genotypes of male is XSY

The genotype of female is XsXs

The genotypes of offsprings are

Straight wing female: XSXs

Curved wing male: XsY

The cross is given below-