Explain with an example how single genes affect multiple traits and alleles the phenotype of an organism.

Explanation

When one gene influences two or more unrelated characteristics or phenotypic traits, the gene is called pleiotropic gene. Such a gene exhibits multiple phonotypic expressions.
An example of pleiotropy is phenylketonuria, an inherited disorder in human being. This is due to the increase of an amino acid phenylaalanine in the body, which can be very dangerous. The disease is caused by a defect in a single gene, that codes for enzyme phenylalanine hydroxylase, that affects multiple systems such as the nervous and integumentary system. Other examples of pleiotropy are albinism, sickle cell anemia and schizophrenia in human beings.