What is the term used when two alleles are identical?

The term used when two alleles are identical is homozygous. In genetics, an organism is described as homozygous for a particular trait if it carries two copies of the same allele, whether dominant or recessive. This creates uniformity in the genetic makeup for that specific trait, which can have significant implications for the phenotype expressed.

For instance, if a horse has two alleles for a specific coat color that are both the same, it will exhibit that coat color consistently. This concept is essential in genetics as it relates to inheritance patterns and can influence breeding decisions, as homozygous individuals can produce offspring with predictable traits when bred together.

In contrast, when alleles are different, the organism is termed heterozygous, which can lead to a variety of traits being expressed, depending on dominance and other genetic factors. The terms polygenic and monomorphic refer to different genetic situations unrelated to the identity of alleles; polygenic involves multiple genes affecting a trait, while monomorphic pertains to a single allele being present in a population, affecting its variability. Understanding these distinctions is vital for genetic study and applications in horse evaluation.