In genetics, what do we call the allele that is expressed in the phenotype?

The term used to describe the allele that is expressed in the phenotype is the dominant allele. This is because dominant alleles can mask the effect of recessive alleles when both are present in a heterozygous organism. If an organism carries two different alleles for a trait, the phenotype will reflect the trait corresponding to the dominant allele. For example, in a pair of alleles where one is dominant (for a brown eye color) and the other is recessive (for blue eye color), the organism will express the brown eye phenotype because the brown allele is dominant.

In contrast, recessive alleles only show their effects when an organism is homozygous for that trait, meaning it has two copies of the recessive allele. If a dominant allele is present, its impact overshadows that of the recessive allele, so that recessive traits do not manifest in the phenotype. Codominant alleles, on the other hand, can both be expressed in the phenotype simultaneously, as seen in certain blood types, but only one of them is considered dominant in a simple dominant-recessive relationship. Lastly, the term "simplistic allele" is not recognized in genetic terminology and does not apply to the concept being discussed. Thus