Blood Groups: ABO

✅ABO grouping is based on the presence or absence of two surface antigens (chemicals that can induce immune response) on the RBCs namely A and B.

✅Similarly, the plasma of different individuals contain two natural antibodies (proteins produced in response to antigens).

✅ABO blood groups are controlled by the gene I. The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the kind of sugar is controlled by the gene. The gene (I) has three alleles IA, IB and i.

✅The alleles IA and 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.

✅IA and IB are completely dominant over i, in other words 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 co-dominance. Hence red blood cells have both A and B types of sugars.