nonpenetrance

The state in which a genetic trait, although present in the appropriate genotype ( i.e., homozygous, hemizygous, or heterozygous according to the state of dominance and mode of inheritance), fails to manifest itself in the phenotype because of modifying factors. Cf.:hypostasis.

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non·pen·e·trance (non-penґə-trəns) in genetics, lack of phenotypic expression of a particular genotype by an individual. Cf. penetrance.