The extent to which an expressed gene manifests its effect in an organism.
Expressivity refers to the influence of an expressed gene in individuals. A variable expressivity pertains to the consistency of the gene’s influence on the individual. It occurs when a phenotype is expressed but to a different degree among individuals with the same genotype. For example , some individuals suffering from Marfan disease have long fingers and toes. Others would have a full blown disease with the dislocation of the lens and dissecting aneurysm of the aorta.
Synonym: genetic expressivity