Question

A diseased man marries a normal woman. The couple has 3 daughters and 5 sons. The daughters are diseased while the sons are normal. The gene of the disease is

• A. Sex-linked recessive
• B. Sex-linked dominant
• C. Autosomal character
• D. Sex-limited character

Answer 1

Answer: (B)

Sex-linked dominant

Genes for sex-linked dominant traits are located on the sex chromosomes or allosomes. They are expressed even when they are present in the heterozygous condition. It is more common in females.

In the given case, the father is deceased. It means father carries the X-chromosome which has the gene for the disease. So, a father can transfer X-chromosomes only to daughter. So, the sex-linked dominant trait will only affect the daughter. The trait can appear in the progeny which are heterozygous. Examples of diseases caused by sex-linked dominant genes are hypophosphatemic rickets, oral-facial-digital syndrome type I and fragile X syndrome.