A man with normal vision who is a dwarf due to achondroplasia has children with a woman with colorblindness who is of average height. Dwarfism caused by achondroplasia is autosomal dominant, and red-green color blindness is X-linked recessive. What proportion of their daughters are expected to be color-blind with achondroplasia?
A) 0
B) 1/2
C) 1/4
D) 3/4

Question

Quizplus · Accepted Answer

Since achondroplasia is autosomal dominant, the man must have one allele for achondroplasia and one normal allele. For color blindness, which is X-linked recessive, the woman must have two alleles for color blindness (since she is colorblind and females have two X chromosomes). Daughters inherit one X chromosome from their mother and one from their father. All daughters will inherit the X chromosome carrying the normal vision allele from their father (since he is not colorblind and males have only one X chromosome), ensuring they are not colorblind. They will also inherit one allele for achondroplasia from their father, making them affected by achondroplasia. However, since the question asks specifically for daughters who are both color-blind and have achondroplasia, and we've established that all daughters will not be color-blind, the correct answer is 0.

A Man with Normal Vision Who Is a Dwarf Due