Inheritance of Blood Groups


 
 
Concept Explanation
 

Inheritance of Blood Groups

How Blood Groups are Inherited

  • A person has one of the four blood groups : A, B, AB or O.
  • This blood group system is controlled by a gene which has three different forms denoted by the symbols I^A,I^Band I^O. The genes I^A and I^B show no dominance over each other, that is, they are co dominant. However genesI^A and  I^Bboth are dominant over the gene I^O. In other words, the blood geneI^O  is recessive in relation to genes I^A andI^B .  
  • Although there are three genes (or three gene forms) for blood, but any one person can have only two of them. So, the blood group of a person depends on which two forms of the genes he poses.
  • If the genotype (gene combination) isI^AI^A , then the blood group of the person is A. And if the genotype is I^A I^Oeven then the blood group is A (because I^O is a recessive gene).
  • If the genotype is I^B , then the blood group of the person is B. And if the genotype is I^BI^O even then the blood group is B (because I^O is a recessive gene)
  • If the genotype isI^AI^B , then the blood group of the person is AB.
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    Sample Questions
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    Question : 1

    Which of the following are correct ?

    (a) A person can have one of the four blood groups  A, B, AB or O.

    (b) The genes I^A and I^B show no dominance over each other, that is, they are co dominant. 

    Right Option : C
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    Question : 2

    Which of the following are correct ?

    (a) A person can have one of the four blood groups: A, B, AB or O.

    (b) The blood group system is controlled by a gene which has three different forms denoted by the symbols I^A,I^Band I^O.

    (c) If the genotype (gene combination) isI^AI^A , then the blood group of the person is O .

    Right Option : A
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    Question : 3

    The genotype (gene combination) of man’s blood isI^A I^O  and that of woman’s blood isI^OI^O in this case there is an equal chance that the genotype of child’s blood can be either ______________________ .

    Right Option : B
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