Question

Three alleles namely IA, IB and i could blood grouping in human beings. How many genotypes are likely to be present in the human population
A. 2
B. 4
C. 5
D. 6
E. 7

Answer 1

Hint: ABO blood group in humans is controlled by genes and it has three alleles: IA, IB and i. As there are three different alleles, different genotypes are possible.

Complete answer: ABO blood groups are controlled by the gene I. The plasma membrane of the red blood cells has sugar polymers and the kind of sugar is controlled by the gene. The gene (I) has three alleles IA, IB and i. The alleles IA, IB produce a slightly different form of the sugar while allele i does not produce any sugar. Because humans are diploid organisms, each person possesses any two of the three I gene alleles. When IA and i are present, only IA expresses (because i does not produce any sugar), and when IB and i are present, IB expresses. But when IA and IB are present together, they both express their own types of sugars: this is because of codominance. So, red blood cells have both A and B types of sugars. Since there are three different alleles, there are six different combinations of these three alleles that are possible, and therefore, a total of six different genotypes of the human ABO blood types.
Six possible genotypes are: IA IA , IA i, IB IB , IB i, IA IB , ii.
Therefore, option D is the correct answer.

Note: AB group was discovered by De Castello and Steni. Bernstein proved that these groups are controlled by three alleles: IA, IB and i. The alleles follow the Mendelian pattern of inheritance. A blood group of individuals are also known as universal donors, while AB blood groups are known to be universal acceptors.