GENETIC PROBLEMS

GENETIC PROBLEMS - Sex-Linked Inheritance

BIOL 1406

Colorblindness (X^c) and hemophilia (X^h) are both recessive sex-linked traits in humans. The dominant allele of the colorblindness trait is for normal color vision (X^C). The dominant allele of the hemophilia trait is for normal blood clotting (X^H).

1. Give the genotype of each of the following individuals:

Male with normal color vision _________________ X^CY

Female with normal colorblindness _____________ X^CX^c

Female who is colorblind ____________________ X^cX^c

Male with normal blood clotting _______________ X^hY

Female with normal blood clotting _____________ X^HX^H

Female carrier of hemophilia _________________ X^HX^h

2. A woman who is a carrier of the hemophilia gene marries a man who has normal clotting blood. What are the possible genotypes of their daughters? What are the possible genotypes of their sons?

Woman = X^HX^h Man = X^HY

Daughter Genotypes = X^HX^H or X^HX^h

Son Genotypes = X^HY or X^hY

3. A man who is colorblind marries a woman who is a carrier of the colorblind gene. What is the percentage chance that one of their sons would be colorblind? What is the chance that one of their daughters would be colorblind?

Man = X^cY Woman = X^CX^c

	X^c	Y
X^C	X^CX^c	X^CY
X^c	X^cX^c	X^cY

% Chance of colorblind son = 1/2 = 50%

% Chance of colorblind daughter = 1/2 = 50%

4. A woman who is a carrier of the colorblindness gene marries a man who has normal color vision. What is the chance they will have a son who is colorblind? Chance of a daughter who is a carrier? Chance of a daughter who is colorblind?

Woman = X^CX^c Man = X^CY

	X^C	X^c
X^C	X^CX^C	X^CX^c
Y	X^CY	X^cY

% Chance of colorblind son = 1/2 = 50%

% Chance of carrier daughter = 1/2 = 50%

% Chance of colorblind daughter = 0/2 = 0%

5. A boy, whose parents and grandparents had normal clotting blood, has hemophilia. Give the genotypes for his mother and maternal grandparents.

Boy = X^hY Mother = X^HX^h (she is a carrier)

Maternal Grandmother = X^HX^h (she is a carrier)

Maternal Grandfather = X^HY (he has normal clotting)

6. A brown-eyed young man whose mother was color-blind and whose father had blue eyes is engaged to marry a young woman whose color-blind mother had blue eyes and whose normal-vision father had blue eyes. What is the genotype of the young man? Of his fiancée? If they marry and have a family, what are the chances of having: A brown-eyed normal vision daughter? A blue-eyed colorblind son? A colorblind brown-eyed daughter?

Young Man = Bb X^cY (he is colorblind with brown eyes)

Young Woman = bb X^CX^c (she is a carrier with blue eyes)

	BX^c	BY	bX^c	bY
bX^c	BbX^cX^c	BbX^cY	bbX^cX^c	bbX^cY
bX^C	BbX^CX^c	BbX^CY	bbX^CX^c	bbX^CY

Brown-eyed, normal vision daughter = 1/8 = 12.5%

Blue-eyed, colorblind son = 1/4 = 25%