What are identical alleles on homologous chromosomes referred to as?

Identical alleles on homologous chromosomes are referred to as homozygous. In genetics, an individual is described as homozygous for a particular gene if both alleles — one inherited from each parent — are the same. This means that there is no variation in the genetic information for that specific gene on the homologous chromosomes, which can significantly impact traits expressed in an organism.

When an organism is homozygous for a trait, it can lead to the expression of a specific phenotype under the influence of that gene, without interference from other variants of the allele. In contrast, if the alleles were different, the organism would be considered heterozygous for that trait, which often leads to a mix of traits expressed or dominance scenarios where one allele may mask the effect of the other.

The terms hemizygous and polygenic refer to different genetic concepts. Hemizygous typically describes individuals who have only one allele for a gene, such as males regarding X-linked genes, while polygenic refers to traits that are controlled by multiple genes, rather than a single gene. Thus, the concept of being homozygous specifically pertains to the identical nature of alleles on homologous chromosomes.