Heterozygous eye color alleles led the boy to look like his brown-eyed mother but not his blue-eyed father.

If both gene alleles are different, the organism is heterozygous for that particular trait.

Since sickle cell disease requires two alleles that are alike, a person with a heterozygous would not have the disease.

With one dominant allele and one that is recessive, the heterozygous gene pair brought forth a baby with red hair.

Heterozygous carriers of two independent alleles in the same gene often have the trait that is dominant of the two.