Question

The probability of the male child of a haemophilic father and a normal mother becoming haemophilic is

• A. 25%
• B. 0%
• C. 50%
• D. 100%

Answer 1

Answer: (B)

Haemophilia is an X-linked recessive disorder. Since father transmits its X chromosome to the daughters, not to son, so the haemophilic father would not affect the disease inheritance of his son. Son receives its X chromosome from mother which means that the mother should have at least one copy of affected allele to transmit the disease to her son. Mother with both normal copies of X-chromosome will have all normal sons.

So, the correct answer is option B.