Question

In the given pedigree chart, a cross between a normal couple resulted in a son who was haemophilic and a normal daughter. In course of time, when the daughter was married to a normal man, to their surprise the grandson was also haemophilic.

Choose the option that indicates the correct inheritance of trait in the above pedigree chart:

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

Hint:

Sex-linked recessive traits like haemophilia often affect males more because they have only one X chromosome. Carrier females can pass the gene to their sons.

Answer 1

The Correct Option is D

Step 1: The trait (haemophilia) is seen only in males and skips a generation, as the daughter of the affected male is a carrier (normal phenotype) but passes the trait to her son.
Step 2: This suggests the trait is inherited through the X chromosome, and since females are generally carriers while males are affected, it fits the pattern of a sex-linked recessive trait.
Step 3: If it were dominant or autosomal, affected females would appear more frequently or the inheritance pattern would not be restricted by gender as seen here.