Expressivity; qualitatively the
Expressivity is a term used in genetics that refers to variations of a phenotype in individuals carrying a particular genotype. The term is used to qualitatively characterize the variance or extent of the phenotype given a particular genotype. For example, the “blue” gene might have an expressivity of 25% for individuals that express the “blue” gene and appear light blue, and 75% for individuals that express the “blue” gene and appear dark blue. This differs from penetrance in that penetrance refers to the likelihood of the gene generating any phenotype at all, while expressivity refers to the influence of an expressed gene in individuals. Variable expressivity occurs when a phenotype is expressed to a different degree among individuals with the same genotype. For example, individuals with the same allele for gene involved in a quantitative trait like body height might have large variance (some are taller than others), making prediction of the phenotype from a particular genotype alone difficult. The expression of a phenotype may be modified by the effects of aging, other genetic loci or environmental factors.
See also
- Penetrance
- Allele
- Phenotype
- Genotype
- Mendelian inheritance