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One child is haemophilic (sex-linked trait), while its fraternal twin brother is normal. Which one of the following informations is most appropriate?
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- The mother must have been heterozygous
- The child is a monozygotic twin
- The other child is a female and the father is haemophilic
- The haemophilic child is a male
Correct Option: A
The mother must have been a haemophilic carrier (XhX). 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.
