Principles of Inheritance and Variation Question 188
188. One child is haemophilic (sex-linked trait), while its fraternal twin brother is normal. Which one of the following informations is most appropriate?
[1999]
(a) The mother must have been heterozygous
(b) The child is a monozygotic twin
(c) The other child is a female and the father is haemophilic
(d) The haemophilic child is a male
Show Answer
Answer : a
Hints & Solution
(a) The mother must have been a haemophilic carrier $(X^{h} X)$. One of the twins would have inherited the normal $X$ chromosome and the other would have received the $X$ chromosome carrying the gene for haemophilia.
