Q160 / 180 · NEET 2020 (Phase 1) · Zoology

Identify the wrong statement with reference to the gene ‘I’ that controls ABO blood groups.

  • A
    A person will have only two of the three alleles.
  • Correct answer
    B
    When IA and IB are present together, they express same type of sugar.
  • C
    Allele ‘i’ does not produce any sugar
  • D
    The gene (I) has three alleles.

Solution

For the ABO system of blood groups, allele IA produces N acetylgalactosamyl transferase enzyme which recognizes H antigen present in RBC membrane and adds N-acetylgalactosamine to sugar part of H antigen to form A antigen. The allele IB produces galactosyl transferase enzyme which adds galactose o the sugar part of H antigen to form B antigen. Allele 'i' does not produce any sugar or antigen. When both IA and IB are present in a person, both enzymes thus both antigens A and B are produced. This is because of co-dominance. These antigens determine the type of AB blood group. 

Hence, the correct answer is option: 'B'.

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