When alleles of a gene pair are different, they are said to be:

When alleles of a gene pair are different, they are referred to as heterozygous. This genetic condition describes an individual who possesses two different alleles for a specific gene, one inherited from each parent. For example, if one parent contributes an allele for brown eyes and the other contributes an allele for blue eyes, the offspring would be heterozygous for the eye color gene.

Heterozygosity can lead to a variety of traits being expressed, depending on the dominance relationships between the alleles. In contrast, homozygous refers to having the same alleles for a gene pair (e.g., two brown eye alleles), codominant refers to a situation where both alleles in a heterozygous pair are fully expressed (like in AB blood type), and epistatic pertains to one gene masking or modifying the expression of another gene, which is a different concept altogether. Understanding these terms is fundamental in genetics, as they provide insight into inheritance patterns and trait expression.