An allele whose presence will determine the phenotype, regardless of the nature of its companion allele.

Characteristic associated with genes that are reflected in the phenotype both in the homozygous and the heterozygous state (e.g., only one copy of the dominant allele is required to give the characteristic).

A characteristic determined by an allele that is expressed over any other alleles for a given trait.

a trait controlled by an allele that expresses itself even when heterozygous

The variation of a specific, identifiable gene that results in observable traits. For example, tall is a dominant trait in pea plant growth. They cross with bush varieties will usually result in tall varieties. See also "trait."