ABO blood groups in humans are controlled by the gene I.

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ABO blood groups in humans are controlled by the gene I. It has three alleles – I^A I^B and i. Since there are three different alleles, six different genotypes are possible. How many phenotypes can occur?

1. Three
2. One
3. Four
4. Two

Correct Option: C

The three alleles in ABO blood groups in humans can produce six different genotypes and four different phenotypes.
Genotypes      Phenotypes
I^{A^{,I^{A^{, I^{A^{i      Blood group A
I^{B^{I^{B^{, I^{B^{i      Blood group B
I^{A^{I^{B^{Blood group AB
ii      Blood group O}}}}}}}}}}}}}}}}