What is the term for an organism that has two different alleles for a trait?

An organism that has two different alleles for a trait is referred to as heterozygous. In a heterozygous condition, one allele is inherited from one parent and another allele, which is different, is inherited from the other parent. This genetic variation can influence how traits are expressed, particularly in traits governed by dominance, where one allele may mask the effect of the other.

In contrast, the term homozygous refers to an organism that has two identical alleles for a trait. The terms dominant and recessive refer to the relationship between alleles and how traits are expressed, rather than the number or similarity of alleles present. Dominant alleles can mask the effect of recessive alleles, but they do not determine whether an organism is heterozygous or homozygous. Hence, heterozygous is specifically used to describe the scenario of having two different alleles.