Characteristic associated with genes that are reflected in the phenotype only in the homozygous state (e.g., both copies of the recessive allele are necessary to produce the characteristic).

An allele that affects the phenotype only when the individual is homozygous for that trait.

a trait for which two copies of the gene must be present for the trait to be seen

A characteristic determined by an allele that requires the presence of two identical alleles to be expressed.

a trait controlled by an allele that does not express itself in the heterozygous condition

The variation of a specific, identifiable gene that results in observ able traits only if the dominant trait is not present. For example, wrinkled pea seeds result only in varieties where the dominant smooth-seed trait is missing.

A trait that is expressed only when two copies of the gene responsible for the trait are present.