Question

A diseased man marries a normal woman. They get three daughters and five sons. All the daughters were diseased and sons were normal. The gene of this disease is

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

Answer 1

The correct option is A Sex linked dominant

Father transmits his "X-chromosome" to the daughter while the sons receive "Y-chromosome" from father. Since only daughter and none of the sons are affected, the trait is X-linked. Daughters get the second copy of X-chromosomes from the mother who is normal and hence does not carry the affected allele of the trait. The trait is expressed in daughters under heterozygous condition, hence it is a X-linked dominant trait. The correct option is A.