A man who is a dwarf with achondroplasia and normal vision marries a colour-blind woman of normal height. The man's father was six feet tall, and both the woman's parents were of average height. Dwarfism caused by achondroplasia is autosomal dominant, and red-green colour blindness is X-linked recessive. What proportion of their sons would be colour blind and of normal height?
A) none
B) half
C) one out of four
D) all

Question

Quizplus · Accepted Answer

The sons will inherit the Y chromosome from their father and one X chromosome from their mother. Since the mother is color-blind (homozygous recessive for the X-linked trait), all sons will be color-blind. The father is a dwarf due to an autosomal dominant trait, but since the father is heterozygous (his father was of normal height), there is a 50% chance that the sons will inherit the normal height allele. Thus, half of the sons will be color-blind and of normal height.

A Man Who Is a Dwarf with Achondroplasia and Normal