Question

1) A woman who is heterozygous for an X-linked recessive disease gene has many children with a man who has the disease (assume the disease is due to a single gene). Which answer below will most likely describe the phenotypes of their children?

A) all the sons will be normal all the daughters will be carriers

B) all the sons will be carriers all the daughters will be normal

C) all the sons will be normal and all the daughters will have the disease

D) half the sons will have the disease and half the daughters will be normal

4) A woman with blood type A marries a man with blood type B. The woman's parents are blood type AB and O. The man's parents are both blood type B, but he has a full sister that has blood type O (full sister, means that she's not a half sister, she shares both parents with the man). Given this information, what is the probability that the woman and the man will have a daughter, and that this daughter will have blood type A?

A) 1/4

B) 1/12

C) 1/8

D) 1/6

Answer 1

1) let assume the defected gene is a

then the genotype of woman will be X^aXand the man will have X^aY

X^aX    X X^aY

	Xa	X
Xa	Xa Xa daughter with disease	XaX daughter, carrier
Y	XaY son with disease	XY son, normal

D) half the sons will have the disease and half the daughters will be normal

4) let start with the genotype of the full sister of the man. She has O blood group, thus the genotype= I^oI^o

Now, both the parent of the man has blood group B. Now looking at their daughter, both the parent must have carried one I^o. Thus the genotype of the parent is I^BI^o

The man is having the blood group B, looking at the genotype of his parent which is I^BI^o for both

I^BI^{o X} I^BI^o

there are two possibility, the man either have I^BI^o orI^BI^B

Now coming to the woman, her parents are having AB and O blood group. Thus the genotype of her parent is I^A I^B for AB and I^oI^o for for O blood group.

As the woman is A, her genotype will be I^AI^o.

when we crossed I^A I^o X I^B I^B

there will have no daughter with A blood group

	IA	Io
IB	IA IB AB	Io IB B
IB	IA IB AB	Io IB B

however if the cross is between I^AI^o. X I^BI^o

there is a possibility of A) 1/4 daughter will have blood group tyoe A

	IA	Io
IB	IA IB AB	IB Io B
Io	IA Io A	Io Io O