Question

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

Answer 1

Answer: None of their daughters.

Explanation: For the purposes of this exercise, we shall take it as a given that red-green color blindness has an X-linked recessive inheritance pattern. Since the man (who possesses only one X chromosome) does not have color blindness, we can assume that he is not a carrier of a pathogenic allele for this trait. His female partner, in contrast, does have the disease despite being in possession of two X chromosomes and we can therefore assume that each of those X chromosomes contains a pathogenic allele.

Each of the couple's potential daughters will inherit two X chromosomes. The one inherited from the father's side will contain a normal allele (barring the potential for de novo mutations), while the one inherited from their mother will contain a pathological allele. Since it takes two affected alleles for the disease to become manifest, those daughters will be merely asymptomatic carriers.

In conclusion: none of the daughters (affected by dwarfism, or otherwise) will be colorblind.