Which of the following describes an organism with two different alleles at a locus?

An organism with two different alleles at a locus is referred to as a heterozygote. In genetics, alleles are different forms of a gene that can exist at a specific locus on a chromosome. When an organism has two different alleles for a particular gene, it means that one allele may be inherited from one parent, while the second allele is inherited from the other parent, leading to a heterozygous condition.

This is distinct from a homozygote, where an organism possesses two identical alleles at a locus. Genotype refers to the genetic constitution of an organism, which can include both heterozygous and homozygous conditions, whereas phenotype is the observable traits or characteristics of an organism resulting from the interaction of its genotype with the environment. Thus, the term that specifically describes an organism with two different alleles is heterozygote.