In a cross between a normal male and a female carrier for haemophiliac disease, the...

Explanation

This Biology question is asking about the percentage of sons that are expected to inherit haemophilia, a genetic disorder that affects blood clotting, when a male with normal blood clotting ability mates with a female carrier of the haemophilia gene. The correct answer is Option B: 50%. This is because haemophilia is an X-linked recessive disorder, which means the gene for haemophilia is carried on the X chromosome. Males have one X and one Y chromosome, while females have two X chromosomes. If a female is a carrier of the haemophilia gene on one of her X chromosomes, she has a 50% chance of passing that X chromosome on to her son. If her son inherits the haemophilia gene, he will suffer from the disease because he does not have a second X chromosome to provide a healthy copy of the gene. It's important to note that females can also inherit haemophilia if they inherit the haemophilia gene on both of their X chromosomes. However, this is much less common than in males because females have a second X chromosome that can provide a healthy copy of the gene. In summary, when a normal male mates with a female carrier of haemophilia, there is a 50% chance that their son will inherit the haemophilia gene and suffer from the disease. Daughters have a 50% chance of inheriting the gene and becoming carriers themselves, but are unlikely to suffer from the disease unless they inherit the gene on both X chromosomes.