Question

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

Answer 1

Answer: (C)

Sex-linked recessive

Parents are not showing any signs of inherited disease but sons do show. Hence, it cannot be autosomal or sex-linked dominant disease as dominant mode of inheritance is seen in all the generations. The mode of inheritance of given inherited disease is sex-linked recessive and the defective gene is present on the X chromosome. In the given case, father is having normal genotype, XY. Mother is carrier of the disease, that is she is having one defective X chromosome. All daughters will receive at least one normal copy of X chromosome from father. Hence, none of them shows signs of inherited disease. However, three out of five sons received defective X chromosome from mother and suffered from disease. Other two sons received normal X chromosome from mother and showed no signs of disease.

Thus, the correct answer is option C.