Expressivity is a term used in genetics that refers to variations of a phenotype in individuals carrying a particular genotype. The term can be used to qualitatively or quantitatively characterize the extent of the phenotype variation given a particular genotype. The term is equivalent to the severity of a condition in clinical medicine. For example, the amount of blood ejected from the pumping heart with each contraction can be quantitated by echocardiography and is called the ejection fractio… (More on Expressivity)