AP BIOLOGY

Detailed explanation-1: -Here Man is hemophilic which means his X chromosome is defective, and the mother is normal, so in the son X chromosome definitely comes from mother, but not from father so the answer is 0%. Hence, the correct answer is option (D).

Detailed explanation-2: -It is caused by a recessive gene located in the X-chromosome. When a haemophilic man (XhY) marries a normal woman (XX), produces carrier girls (XXh) and normal boys (XY), i.e. all their offsprings will be normal. So, the probability to have haemophilic daughter will be 0%.

Detailed explanation-3: -Each daughter has a 1 in 2 (50%) chance of getting her mother’s hemophilia allele and being heterozygous. Overall, there is a 1 in 4 (25%) chance for each pregnancy that the baby will be a son with hemophilia and a 1 in 4 (25%) chance that the baby will be a heterozygous daughter.

Detailed explanation-4: -So, the correct answer is ‘50% sons will have haemophilia’.

Detailed explanation-5: -It is evident from the above cross that the probability of having a haemophilic son (XhY) is 50% as the other son will not suffer from this disorder.