Effect of single gene on multiple phenotypic expressions.
e.g. size of the starch grains produced and shape of the seeds in pea plant are controlled by a single gene // Phenylketonuria characterised by mental retardation and reduction in hair and skin pigmentation.
Detailed Answer:
The ability of a gene to have multiple phenotypic effects because it influences more than one trait or a number of characters simultaneously is called pleiotropism and such genes are known as pleiotropic genes, e.g. in man a gene producing the *** phenylketonuria also produces a number of abnormal phenotypic traits such as short stature, mental retardation widely spaced incisors, pigmented patches on skin etc. Another such example is the size of starch grains produced and shape of the seeds in pea plant are controlled by a single pleiotropic gene. In Drosophila the gene for vestigial wings also affects structure of reproductive organs and the bristles on the wings.
