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Other Pattern Of Inheritance

 

Inheritance of Blood Groups

  • Bernstein explained the mechanism of inheritance of ABO blood groups. Inheritance of human blood groups is an example of multiple allelism. It is the result of the expression of three genes, which occupy the homologus locus on the same chromosome. The three genes involved in the expression of blood groups are represented by using a common symbol I (abbreviation of isohemoagglutination).
  • The gene which is responsible for the production of antigen A is represented as IA.
  • The gene which is responsible for the production of antigen B is represented as IB.
  • The gene which is responsible for the absence of both the antigens is represented as I°. This gene (I°) is recessive to both IA and IB. Hence, it can express only in the homozygous condition (I°I°).
  • The gene IA is dominant over I° but not over IB. Similarly, the gene IB is dominant over I° but not over IA. Hence, when the genes IA and IB are present together, both antigens are produced. This phenomenon is known as codominance.
  • Blood groups A and B can express either in homozygous or heterozygous conditions.
  • Blood group AB is expressed only in a heterozygous condition.
  • Blood group O is expressed only in a homozygous condition because it is recessive to both A and B.

shows different types of blood groups and their genotype.

 

 

 

Blood Groups

Genotypes

A

IAIA or IA

B

IBIB or IB

AB

IAIB

O

I°I°





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