If a female, looking apparently normal but being carrier of haemophilia, marries a normal male and if two sons and two daughters are born to them, then what would be the probability of manifestation of haemophilia among the children?
(a) 100% haemophilic son and 0% haemophilic daughter
(b) 50% haemophilic son and 50% haemophilic daughter
(c) 0% haemophilic son and 50% haemophilic daughter
(d) 50% haemophilic son, and 50% apparently normal but carrier daughter
(d) 50% haemophilic son, and 50% apparently normal but carrier daughter.
Explanation:
Haemophilia is an X-linked recessive disorder. A carrier female has one defective X chromosome (XhX), while the normal father has XY.
Possible offspring:
- Sons: Each son has a 50% chance of inheriting Xh from the mother and a Y from the father, making him haemophilic (XhY), or inheriting X from the mother and Y from the father, making him normal (XY).
- Daughters: Each daughter has a 50% chance of being a carrier (XhX) or normal (XX), since she inherits one X from each parent.
So, out of two sons, one is expected to be haemophilic; out of two daughters, one is expected to be a carrier.
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