Define pleiotropy.Explain pleiotropy with suitable example.

Explanation

Pleiotropy (Pleiotropic Genes). The ability of"a gene to have multiple phenotypic effect ecause it influences a number of characters simultaneously is known as pleiotropy. The gene aving a multiple phenotypic effect because of its ability to control expression of two or more haracters is called plew-tropic gene. Pleiotropy is due to effect of the gene on two or more inter elated metaboli pathways that contribute to formation of different phenotypes. It is not essential nat all the traits are equally influenced. Sometimes the effect of a pleiotropic gene is more evident 1 case of one trait (major effect) and less evident in case of others (secondary effect). Occasionally number of related changes are caused by a gene. They are together called syndrome. In cotton a ene for the lint also influences the height of plant, size of the boll, number of ovules and viability of seeds. In Garden Pea the gene which controls the flower colour also controls the colour of the eed coat and presence of red spots in the leaf axils. In human phenylketonuries sickle cell Aneaenia how pleiotropy. e.g., Phenylketonuria (PKU, Folling, 1934). It is an inborn, autosomal, recessive metabolic isorder in which the homozygous recessive individual lacks the enzyme phenylalanine hydroxylase eeded to change phenylalanine (amino acid) to tyrosine (amino acid) in liver. It results in yperphenylalaninemia which is characterised by accumulation and excretion of phenylalanine, henylpyruvic acid and related compounds. L.ack of the enzyme is due to the abnormal autosomal ecessive gene on chromosome 12. This defective gene is due to substitution. Affected babies are normal at birth but within a few weeks there is rise (30-50 times) in plasma phenylalanine level which impairs brain development. Usually by six months of life severe mental retardation becomes evident. If these children are not treated about one third of these children are unable to walk and two-thirds cannot talk. Other symptoms are mental retardation, decreased pigmentation of hair and skin and eczema. Although large amounts of phenylalanine and its metabolites are excreted in the urine and sweat, yet there is accumulation of phenylalanine and phenyl pyruvate in brain that results in its damage. The heterozygous individuals are normal but carriers. It occurs in about 1 in 18000 births among white europeans. It is very rare in other races.