I have two alleles at a loci, like for polydactyly. The dominant gene gives you six fingers on a hand. 20% of the alleles are dominant in a population, the rest are recessive.

But when I look for the numbers of people in a population that haWhat is the probability that a person in that population has six fingers (expresses the phenotype)? Answer 3 places behind the decimal (0.XXX)ve six fingers, I find that there are FAR FEWER than predicted. This is because of penetrance. The degree of penetrance is the probability that a phenotype is expressed given the genotype. The penetrance for this dominant gene is 10%, or ten percent of the people having the genotype for polydactyly express 6 fingers.

A. My wife is heterozygous for ploydactyly. I am homozygous recessive. What is the probability that my kid will actually have six fingers on each hand (expresses the phenotype)? Answer 2 places behind the decimal (0.XX)

B. What is the probability that a person in that population has six fingers (expresses the phenotype)? Answer 3 places behind the decimal (0.XXX)