Question

If a boy is suffering from haemophilia, whom 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

Hemophilia is an inherited bleeding disorder wherein a person lacks or has low levels of certain proteins called “clotting factors”. This results in people bleeding easily as their blood is not able to clot properly.

Haemophilia is a X-linked recessive disorder.
The question states that no one in the mother’s or father’s family suffers from haemophilia. This indicates that no males in the family suffered from haemophilia and they were completely normal as they have only one X chromosome in their allosomes. They cannot be the carriers and hence the disease cannot pass to the boy by any of the males in the family. So, options (a), (b) and (c) can be eliminated.

As it is a recessive disorder, it gets expressed only in homozygous recessive conditions in females, as they have two X chromosomes in their allosomes.
Each female inherits two sex chromosomes from their parents. A female with one altered X chromosome gene has a 50% chance of passing that gene to her children, whether male or female. The presence of this altered gene in one of her X chromosomes makes her typically a “carrier”, implying that she may pass the disease to her offspring without suffering from it herself. Thus, option (d) is the most appropriate answer.