pleiotropy

Process whereby a given gene influences several different observed characteristics of an organism. For example, in the fruit fly Drosophila the vestigial gene reduces the size of wings, modifies the halteres, changes the number of egg strings in the ovaries, and changes the direction of certain bristles. Many human syndromes are caused by pleiotropic genes, for example Marfan's syndrome where the slender physique, hypermobility of the joints, elongation of the limbs, dislocation of the lens, and susceptibility to heart disease are all caused by one gene.