question_answer

If father shows normal genotype and mother shows a carrier trait for haemophilia then

A)  all the female off springs will be normal

B)  all the female, off springs will be carriers

C)  a male offspring has 50% chance of active disease

D)  a female offspring has probability of 50% to have active disease.

Correct Answer: C

Solution :

: Haemophilia is a sex-linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progenies, hence shows criss - cross inheritance pattern. It is genetically due to recessive sex - linked gene h carried by X chromosome. A female becomes haemophiliac only when both its X chromosomes carry the gene \[({{X}^{h}}\,{{X}^{h}})\]whereas in case of males, a single gene for the defect is able to express itself \[({{X}^{h}}\,Y)\]If father is normal (X Y) and mother is carrier \[({{X}^{h}}\,X)\] then the probabilities for active disease in offsprings are illustrated in the cross given below: Hence, a male offspring has 50% chance of active disease.