Question

A man and a women, who do not show any apparent signs of a certain inherited disease, have seven children (2 daughters and 5 sons). Three of the sons suffer from the given disease but none of the daughters are affected. Which of the following mode of inheritance do you suggest for this disease?

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

Answer 1

The correct option is D Sex-linked recessive

Since out of total progeny, only sons are affected but none of the daughters are affected, the disease is sex-linked. Further, both parents are normal but their sons are affected who get their X-chromosome from mother and Y-chromosome from the father. If the disease would be Y-chromosome linked, the father would have shown the symptoms but the father is normal. Hence, the mother is carrying the affected allele on one of her X-chromosomes and the disease being recessive is not expressed in the carrier mother. The unaffected sons must have received the normal copy of X-chromosome from the mother. Thus, the correct answer is option D.