Given below are two statements. One is labelled Assertion (A) and the other is labelled Reason (R).
Assertion (A): There are six different genotypes of human ABO blood types.
Reason (R): Human ABO blood types are determined by three alleles.
In light of the above statements, choose the correct answer from the options given below.

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Both (A) and (R) are true and (R) is the correct explanation of (A).

Both (A) and (R) are false.

(A) is true but (R) is false.

Both (A) and (R) are true but (R) is not the correct explanation of (A).

answer is A.

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Detailed Solution

ABO blood groups are controlled by the gene I. The gene (I) has three alleles, I^A, I^B, and i. The alleles I^A and I^B produce a slightly different form of sugar, while allele i does not produce any sugar. Because humans are diploid organisms, each person possesses two of the three I gene alleles. I^A and I^B are completely dominant over i, in other words, when I^A and i are present, only I^A expresses (because i does not produce any sugar), and when I^B and i are present, I^B expresses. But when I^A and I^B are present together they both express their types of sugars: this is because of co-dominance.

Hence, 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.

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