Pleiotropy

Pleiotropy is the phenomenon in which a single gene affects several apparently distinct traits at the same time, altering more than one part of the organism's phenotype through one shared underlying mechanism. Genes that behave this way are called pleiotropic genes. Mendel himself noticed pleiotropy while working with garden pea: when peas with purple flowers, brown seeds and a dark spot on the leaf axils were crossed with peas having white flowers, light-coloured seeds and no axil spot, all three seemingly unrelated traits - flower colour, seed colour and the leaf-axil spot - were inherited together, as a single unit, because a single gene with dominant and recessive alleles happens to control all three simultaneously. Sickle-cell anaemia in humans is a widely cited human example of pleiotropy: a single mutant haemoglobin allele changes red-cell shape and causes a wh …