Expressivity - Variable Expressivity

Variable Expressivity

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 a 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. Another example is neurofibromatosis, where patients with the same genetic mutation show different signs and symptoms of the disease.