A man who is a dwarf due to achondroplasia and has normal vision marries a color-blind woman of normal height.The man's father was 6 feet tall,and both the woman's parents were of average height.Achondroplasia is autosomal dominant,and red-green color blindness is X-linked recessive.
How many of the couple's daughters might be expected to be color-blind dwarfs?
A)all
B)none
C)half
D)one out of four

Question

Quizplus · Accepted Answer

Since achondroplasia is autosomal dominant, the man must have one allele for achondroplasia and one normal allele. For red-green color blindness, which is X-linked recessive, the woman must have two alleles for color blindness (since she is color-blind and females have two X chromosomes). Daughters inherit one X chromosome from their mother and one from their father. The father's X chromosome is normal (not color-blind) because he has normal vision. Therefore, all daughters will inherit the normal X chromosome from their father and either a color-blind or normal X from their mother, but they will not express color blindness because it is recessive and they have at least one normal allele from their father. For achondroplasia, since it is autosomal dominant, daughters have a 50% chance of inheriting the allele for achondroplasia from their father. However, the question asks specifically for daughters who are both color-blind and dwarfs, which would not occur under these genetic conditions.

A Man Who Is a Dwarf Due to Achondroplasia and Has