Polydactyly is a rare dominant phenotype of the human hands and feet. (a) Polydactyly, characterized by extra fingers, toes, or both, is determined by an allele P The numbers in the pedigree (b) give the number of fingers in the upper lines and the number of toes in the lower. (Note the variation in expression of the P allele.)
[(a) © Biophoto Associates/Science Source.]