(a) Explain Polygenic inheritance and Multiple allelism with the help of suitable examples.
(b) Phenylketonuria is a good example that explains Pleiotropy Justify.

Explanation

(a) Polygennic inheritance is the inheritance of a characteristic that is controlled by more than one gene . Polygenic inheritance can produce unexpected phenotypes (i.e., phenotypes that don't fit with Mendel's expected outcomes besed on independent assoectment of dominant and recessive alleles) Two examples of polygenic inheritance are (i) Skin colour in humans and
(ii) Height in humans.
Multiple allelism : In this more than one alleles govern the same character and phenotype. Example , Human blood group (ABO system), controlled by three different alleles `(I^(A),I^(B)andi)`.
(b) Pleiotropy : In pleiotropy , a single gane can exhibit multiple phenotypic expression . In phenylkatonuria single mutated gene express mental retardation and reduction in hair and skin pigmentation.