A WOMAN WHO IS HETEROZYGOUS FOR THE DISEASE HAEMOPHILIA MARRIES A MAN WHO IS HAEMOPHILIC. WHAT PERCENTAGE OF THEIR OFFSPRING WOULD HAVE THE DISEASE

• A. 0%
• B. 25%
• C. 50% ✓
• D. 75%

The answer to the question is: C. 50%

When a woman who is heterozygous for the disease hemophilia marries a man who is hemophilic, their offspring have a chance of inheriting the disease. Hemophilia is an X-linked recessive genetic disorder, meaning that the gene responsible for the disorder is located on the X chromosome. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). In this scenario, the woman is heterozygous for the disease, meaning she carries one normal allele and one allele for hemophilia on her X chromosome. The man is hemophilic, meaning he has only one X chromosome with the allele for hemophilia.

When these parents have offspring, there are several possible outcomes:

1. Sons:
   • If a son inherits his mother’s normal X chromosome and his father’s affected X chromosome, he will not have hemophilia.
   • If a son inherits his mother’s affected X chromosome and his father’s Y chromosome, he will not have hemophilia but will be a carrier like his mother.
   • If a son inherits his mother’s affected X chromosome and his father’s affected X chromosome, he will have hemophilia.
2. Daughters:
   • If a daughter inherits her mother’s normal X chromosome and her father’s affected X chromosome, she will not have hemophilia but will be a carrier like her mother.
   • If a daughter inherits her mother’s affected X chromosome and her father’s Y chromosome, she will not have hemophilia.

Based on these possibilities, the percentage of their offspring that would have the disease can be calculated.

The correct answer to the question “What percentage of their offspring would have the disease?” is C. 50%.