Who discovered ABO blood group. When was it discovered?

Explanation

Human blood groups show all the possible effects of dominance, codominance and multiple allelism.
The alleles `I^A` and `I^B` are dominant over allele `I^O`. Thus a person with genotype `I^A I^O` or `I^B I^O` have blood group A or B Respectively. This explains the concept of dominance.
The alleles `I^A` and `I^B` are codominant with each other. Thus a person with genotype `I^A I^B` will have blood group AB. This explains the concept of codominance
Blood group ABO exhibit multiple allelism as it shows multiple alternatives or alleles of the same gene that occur in humans. These multiple alleles are all located on the same gene locus on the same chromosome.