Two alleles of a gene which result in distinctly different phenotypes, but when they are both inherited together in an individual (one from the mother and one from the father - called heterozygosity), the individual has both of the phenotypes. For example, if one allele is for red hair and the other allele is for blue hair, then the individual will have patches of blue hair and patches of red hair. (This is in contrast to incomplete dominance, where the individual would inherit a blend of the two alleles and have purple hair).