: Pleiotropic genes are those which have multiple effect ability. A single gene expresses multiple phenotypic characters although the primary effect is only one, e.g., sickle cell anaemia. It results in abnormal type of haemoglobin in the red blood cells due to heterozygous condition. The individual having the heterozygous condition of this trait is resistant to malaria. Homozygous recessive in this case is lethal i.e. it causes the death of the individual.