Genes come in pairs, called alleles, and each pair is located in a specific position (or locus) on a chromosome. If the two alleles at a locus are identical to each other, they are homozygous; if they are different from one another, they are heterozygous.

Like all words with the prefix hetero, heterozygous has to do with things that are different — specifically genes. When alleles are heterozygous they are unalike in some way. Alleles determine the genotype, or genetic structure, of a specific gene. For example, you may have received the allele for brown eyes from your mom and the allele for blue eyes from your dad; that means that you are heterozygous for eye color. Whether an organism's genotype is heterozygous or homozygous helps to determine its appearance (which is called its phenotype).

Definitions of heterozygous
  1. adjective
    having dissimilar alleles at corresponding chromosomal loci
    heterozygous for eye color”
    see moresee less
    having identical alleles at corresponding chromosomal loci
Word Family