Problem 17

A man has six fingers on each hand and six toes on each foot. His wife and their daughter have the normal number of digits (5). Extra digits is a dominant trait. What fraction of this couple's children would be expected to have extra digits?

Because the daughter is normal the man's genotype must be heterozygous for the trait so:

if X = extra digits and x = normal (5) digits then:


50% of the offspring will be polydactylic