Question

A man and a woman, who do not show any apparent signs of a certain inherited disease, have seven children (2 daughters and 5sons).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

Based on the information provided, the most likely mode of inheritance for this disease is:
Sex-linked recessive
Here's the reasoning:
The man and woman do not show signs of the disease, which suggests they are carriers (heterozygous) for the disease gene.
Three out of the five sons are affected by the disease, while none of the daughters are affected. This pattern is consistent with X-linked recessive inheritance.
In X-linked recessive inheritance, the gene responsible for the disease is located on the X chromosome. Males have only one X chromosome, so if they inherit a copy of the disease gene, they will express the disease because there is no corresponding healthy allele on the Y chromosome to mask the effect. Females, on the other hand, have two X chromosomes, so they can be carriers without expressing the disease if they have one normal allele to compensate for the mutated one. This pattern explains why none of the daughters are affected (they received a normal X chromosome from the unaffected mother) and why three out of the five sons are affected (they inherited the X chromosome carrying the disease gene from their carrier mother).
So, based on the inheritance pattern observed in the family, X-linked recessive is the most likely mode of inheritance for this disease.

So, the correct option is (D): Sex-linked recessive