What do we call an organism that has two identical alleles for a particular gene?

An organism that has two identical alleles for a particular gene is referred to as homozygous. This means that both copies of the gene, one inherited from each parent, are the same. For instance, if the alleles for a gene are represented as "AA" or "aa," the organism is homozygous for that particular gene. This genetic configuration can play a significant role in determining the organism's traits since homozygous individuals will consistently express the same trait associated with those identical alleles.

In contrast, heterozygous organisms possess two different alleles for a gene (e.g., "Aa"), which can lead to a variety of traits depending on the dominance of the alleles involved. The terms "dominant" and "recessive" are used to describe the relationship between different alleles rather than the relationship between the alleles themselves. A dominant allele masks the effect of a recessive one in a heterozygous pairing. Hence, understanding these terms and definitions is crucial for interpreting genetic information accurately.