What does heterozygous mean in genetics?

In genetics, the term "heterozygous" refers specifically to having two different alleles for a particular gene or trait. Alleles are different forms of a gene that exist at the same locus on homologous chromosomes. When an individual is heterozygous for a trait, it means that one allele may be dominant and the other allele may be recessive, or they could both contribute to the phenotype in varying degrees, particularly in cases of co-dominance or incomplete dominance.

This contrasts with being homozygous, where an individual has two identical alleles for a trait. The presence of two different alleles allows for genetic variation, which is fundamental to evolution and adaptation within populations. Understanding heterozygosity is crucial, especially when predicting the potential offspring's traits through principles such as Mendelian inheritance.