Question

The best example for pleiotropy is:

• A. Skin colour
• B. Phenylketonuria
• C. Colour Blindness
• D. ABO Blood group

Answer 1

The correct option is B Phenylketonuria

The ability of a single gene to exhibit multiple phenotypic effects because it influences several characters simultaneously is known as pleiotropy.

Example: Phenylketonuria (PKU).

PKU is an inborn error of metabolism. This disease is caused in humans by mutation in the gene that codes for the enzyme phenylalanine hydroxylase. This enzyme converts phenylalanine into tyrosine. Deficiency of this enzyme results in mental retardation, reduction in hair and skin pigmentation.

Human skin colour is a classic example of a polygenic trait. Polygenic inheritance refers to the condition in which one character is controlled by multiple genes and each of them contributes some amount to the overall phenotype. In this case, the cumulative effect of these genes (polygenes) control the expression of the resultant phenotype.

Colour blindness is an X-linked recessive genetic disorder.

ABO blood groups is a very good example of multiple allelism and codominance.