Question

Hemophilia is a sex-linked recessive trait. If a hemophiliac male marries a carrier female, what percent of their daughters will have hemophilia? The gene for yellow body color in Drosophila is recessive and sex-linked. Its dominant allele b+ produces wild-type body color while the recessive allele, b- produces yellow body color in homozygous individuals. List the phenotypes and genotypes of the progeny from the following matings: a. yellow female x wild-type male b. wild-type (carrier) female x wild-type male c. wild-type (carrier) female x yellow male

Answer 1

1. Hemophilic is a sex-linked trait and a recessive disorder. Suppose the dominant allele is h+, and the recessive allele is -h.

It is an X-linked trait, If the male is hemophilic then his genotype is X^-hY, and the female is the carrier of this disease, then her genotype is X^+hX^-h.

Parents- (Male)X^-hY *   (female) X^+hX^-h

Gametes- X^-h Y X ^+h X^-h

F1 generation -

Gametes	X-h	Y
X+h	X-hX+h (carrier female)	X+hY (normal male)
X-h	X-hX-h (hemophilic female)	X-hY (hemophilic male)

Total number of daughters- 2

Hemophilic female - 1

percentage of daughters that are hemophilic is :- (1/2)*100= 50%

2. Yellow body color in Drosophila is a recessive and sex-linked trait.

+b allele is dominant and gives wild type body color, and -b is recessive allele, which gives yellow color in homozygous condition.

a) yellow female X wild-type male

The genotype of yellow female - X^-bX^-b ; gametes- X^-b and X^-b

The genotype of wild-type male - X^+bY; gametes - X^+b and Y

F1 generation-

Gametes	X-b	X-b
X+b	X+bX-b (Wild type body color female)	X+bX-b (wild type body color female)
Y	X-bY (yellow color boy)	X-bY (yellow color boy)

b) Wild-type (carrier) female x wild type male

The genotype of female - X^+bX^-b ; gametes - X^-b and X^+b

The genotype of male - X^+bY ; gametes - X^+b and Y

F1 generation-

Gametes	X+b	X-b
X+b	X+bX+b (wild type body color girl)	X+bX-b (wild type carrier body color)
Y	X+bY (wild type body color boy)	X-bY (yellow body color boy)

c) wild-type (carrier) female X yellow male

The genotype of female - X^+bX^-b ; gametes - X^-b and X^+b

The genotype of male - X^-bY ; gametes - X^-b and Y

F1 generation

Gametes	X-b	X+b
X-b	X-bX-b (Yellow body color girl)	X-bX+b (wild type carrier girl)
Y	X-bY (yellow body color boy)	X+bY (wild type body color male)