Question

1. In humans, hemophilia depends on a recessive allele of a sex-linked gene. Hemophilia is a disease in which the blood fails to clot properly. A man whose father was hemophilic, but whose own clotting time is normal, marries a normal woman with no record of hemophilia in her ancestry. What is the chance of hemophilia in her children?

Answer 1

Factor VIII hemophilia is inherited as X-linked recessive state.

Representation:

Since the affected condition is caused by recessive state, representing Factor VIII affected condition as h, corresponding normal state as H.

Thus, genotypes may be represented as:

· Affected Male: XhY (hemizygous, recessive)

· NormalMale: XHY (hemizygous, dominhnt)

· Affected Female: XhXh (homozygous, recessive)

· Carrier female: XHXh (heterozygous, dominant)

· Normal female: XHXH (Homozygous dominant)

• The man's father is hemophilic. But as it is X-linked trait, the hemizygous genotype will be XHY (As phenotype is normal).
• The woman is normal, with no clotting as family history. Hence, she is not a carrier and has genotype XHXH

XHYx XHXH

F1	Femhle
Male	XH	XH	F2
XH	XH XH	XH XH	Female
Y	XHY	XHY	Male

Thus, no child wil be hemophilic.