Question

If a boy is suffering from haemophilia, which of the following could he have received the gene from? Note: no one in the mother's or father's family suffers from haemophilia.

• A. Father's father
• B. Mother's father
• C. Father's mother
• D. Mother's mother

Answer 1

The correct option is D

Mother's mother

Since the boy receives the Y from the father, he receives the X chromosome (which has the gene for haemophilia) from the mother. She, in turn, would have received it either from her father or her mother! Therefore, the gene could have been from either the mother's mother or mother's father. If the gene was present in the mother's father, then he would have suffered from haemophilia. Since no one in the family suffers from it, it would have to be the mother's mother!