Defnition of Pleiotropy

It is an established fact that a specific gene controls a specific phenotypic trait. This finding is not always true. Studies on ‘gene expression’ have revealed that a gene often influences more than one phenotypic trait.
This phenomenon of multiple effects of a single gene is called pleiotropism. In such a genic influence more conspicuous expression of a phenotypic trait by a gene is called its major effect. If the gene causes other less conspicuous phenotypic changes, it is known as secondary effect. Such genes responsible for multiple effects are called pleiotropic genes. Vestigeal wings in Drosophila are caused by a recessive gene in homozygous condition. A keen observation has shown that this gene affectsother traits as well. They are
(i) the small halters or balancers behind the wing
(ii) structure of reproductive organs
(iii) egg production
(iv) life duration and
(v) bristles on the body.