What does it mean if an organism is described as homozygous?

An organism described as homozygous possesses two identical alleles for a specific gene, which could either be two dominant alleles or two recessive alleles. This condition means that both copies of the gene—one inherited from each parent—are the same, leading to consistent expression of a trait. For example, if a plant has two identical alleles for flower color (such as both being red or both being white), it is homozygous for that trait.

In contrast, an organism that possesses one dominant and one recessive allele would be classified as heterozygous, indicating genetic variation at that locus. Also, an organism with different alleles for a gene is explicitly termed heterozygous, while having no alleles for a particular gene is a condition that is generally not defined in typical genetic contexts. Therefore, the presence of either two dominant alleles or two recessive alleles distinctly defines a homozygous organism.