Dominance : It is the phenomenon where one allele expresses itself exclusive of the presence of other allele, The alleles JA and JB both are dominant over allele i as JA and JB forms antigen A and antigen B respectively but i does not form any antigen. . .
Co-Dominance : It is the phenomenon when the `F_1` generation resembles both the parents, and both the parental characters are expressed simultaneously. Both the alleles JA and JB are co- dominant as both ofthem are able to express themselves in the presence of each other in blood group AB (JAJB) by forming antigen A and B.
Multiple allelism : It is the phenomenon of occurrence of a gene in more than two allelic form on the same locus. The ABO blood groups in humans are determined by three different allelic forms `I^a`,`I^b`and i.
