4.2.1 ABO blood types

. . ABO blood types Multiple allele inheritance of ABO blood groups Blood differs chemically from person to person. When two different incompatible blood types are mixed, agglutination (clumping together) of erythrocytes (RBC) occurs. The basis of these chemical differences is due to the presence of antigens (surface antigens) on the membrane of RBC and epithelial cells. Karl Landsteiner discovered two kinds of antigens called antigen ‘A’ and antigen ‘B’ on the surface of RBC’s of human blood. Based on the presence or absence of these antigens three kinds of blood groups, type ‘A’, type ‘B’, and type ‘O’ (universal donor)were recognized. The fourth and the rarest blood group ‘AB’ (universal recipient) was discovered in by two of Landsteiner’s students Von De Castello and Sturli. Bernstein in discovered that the inheritance of different blood groups in human beings is determined by a number of multiple allelic series. The three autosomal alleles located on chromosome are concerned with the determination of blood group in any person. The gene controlling blood type has been labelled as ‘L’ (after the name of the discoverer, Landsteiner) or I (from isoagglutination). The I gene exists in three allelic forms, I A , I B and I O . I A specifies A antigen. I B allele XII Std Zoology Chapter XII Std Zoology Chapter Principles of Inheritance and Variation Table . Genetic basis of the human ABO blood groups Genotype ABO blood group phenotype Antigens present on red blood cell Antibodies present in blood plasma I A I A Type A A Anti -B I A I o Type A A Anti -B I B I B Type B B Anti -A I B I o Type B B Anti -A I A I B Type AB A and B Neither Anti-A nor Anti-B I o I o Type O Neither A nor B Anti -A and anti - B