Question

A normal couple has seven children($2$ daughters and $5$ sons). Three of the sons suffer from a hereditary disorder but none of the daughters is affected. Which is the inheritance type?

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

Answer 1

The correct option is D Autosomal recessive

In the given problem, the disease is the result of sex-linked recessive genes. As neither man nor woman shows signs of disease it means the woman would be the carrier for the disease. In their children none of the daughters suffer from the disease, while the sons were suffered, it means daughters are also a carrier (i.e. X-linked recessive).
Suppose, genotype of man = X Y
Genotype of woman = Xd X

(d-disease causing gene)

For each delivery, the probability for each combination is 25%. So, among seven children 2 normal daughters, 3 diseased sons, and 2 normal sons are possible.

So, the correct answer is 'Sex-linked recessive'.