Question

All the sons are hemophilic and daughters are normal of a haemophilic mother and normal father. What is this character called as?

• A. X linked recessive
• B. Y linked recessive
• C. X linked dominant
• D. Y linked dominant

Answer 1

Answer: (A)

X linked recessive

In X-linked dominant trait, a dominant gene is carried on the X chromosome. X-linked dominant traits do not necessarily affect males more than females. However, X-linked recessive traits are more common among males than females because females have two copies of the X chromosome and males have only one X chromosome. Hence, male requires only one copy of defective gene and female requires two copies of defective gene to show the trait. Hemophilia is X-linked recessive trait. In the given example, father is having genotype XY and mother is having genotype X${}_h$X. Sons are getting X${}_h$ gene from mother and Y gene from father and hence are all hemophilic. Daughters are getting X gene from father and either X or X${}_h$ gene from mother. Hence all daughter are normal phenotypically.

Thus, the correct answer is option A.