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Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYPrinciples of Inheritance and Variation4 Marks
Question
  1. Explain Polygenic inheritance and Multiple allelism with the help of suitable examples.
  2. "Phenylketonuria is a good example that explains Pleiotropy." Justify.
✓

Answer

  1. Traits that are generally controlled by three or more genes , the phenotype reflects the contribution of each allele/effect of each allele is additive 

eg. Human skin colour, controlled by three genes (A , B, C)

In multiple allelism more than two alleles , govern the same character/phenotype  eg . Human blood group (ABO system) , controlled by three different alleles (IA , IB, i)

  1. In pleiotropy a single gene can exhibit multiple phenotypic expressions , in phenyl ketonuria single mutated gene express mental retardation and reduction in hair and skin pigmentation.

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