Expressivity
The intensity or variability with which a genetic trait manifests.
📖 Full definition
Two people may carry the same allele yet express it to very different degrees. This is expressivity: variable between individuals, depending on environment, other genes, epigenetics. To be distinguished from penetrance (presence vs absence of the trait).
💡 Concrete example
Two brothers carrying the same eye-colour allele may have different shades (light green vs dark green) — variable expressivity.
🔗 See also
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