PLEIOTROPISM

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• Pleiotropy refers to the situation in which a single gene influences more than one phenotypic trait.
• Most genes, if not all have their multiple effects and are called pleiotropic genes.
• The phenomenon of multiple effect (multiple phenotypic expressions of a single gene is called pleiotropism)
• Even though a structural gene may have many end effects, it usually has only one primary function, of producing one polypeptide. This polypeptide may give rise to different expressions at the phenotypic level.

Examples of pleiotropism

1.     In Drosophila the recessive gene for vestigial wings causes vestigial wings in homozygous condition and also effects other traits like:

Ø The tiny wing like balancer behind the wing

Ø Certain bristles

Ø The structure of reproductive organs

Ø Egg production is lowered

Ø Longevity is reduced

2.     In Drosophila the gene for white eyes may affect shape of sperm storage organs in females and also some other structures

3.     In human beings the gene for disease phenylketonuria has pleiotropic effect and produce various abnormal phenotypic traits. The affected individuals secrete large amount of an acid phynylalanine in their urine, cerebrospinal fluid and blood. They are short statured, mentally deficient with widely spaced incisors, pigmented patches on skin with excessive sweating and with non-pigmented hairs and eyes.

·      Pleiotropic genes must be more common because indirectly every gene may be involved in the expression of more than one trait. Thus most genes are pleiotropic IN NATURE