A normal girl, whose mother is haemophilic marries a male with no ancestral history of haemophilia. What will be the possible phenotypes of the offspring? Choose the most appropriate answer from the options given below:
- B and D only
- A and B only
- B and C only
- A and D only
Answer
(3) B and C only
Solution
Haemophilia is a sex-linked recessive disorder. Let Xh carry the haemophilia allele.
∵ The mother of the girl is haemophilic (XhXh), the normal girl must be a carrier (XhX).
The male has no history of haemophilia ⇒ normal (XY).
Cross: XhX XY
⇒ Daughters: XhX (carrier) and XX (normal) — no daughter can be haemophilic.
⇒ Sons: XhY (haemophilic) and XY (normal).
∴ Possible offspring: haemophilic son and carrier daughter (B); normal daughter and normal son (C). A and D are not possible as a daughter cannot be haemophilic.
Answer: (3)