Some genes have more than two alleles, and then the pattern of inheritance is called multiple allele inheritance or multiple allelism. However, the basic rules are just the same – alleles can be dominant or recessive or codominant, or incompletely dominant. In the human blood group (ABO) we see the occurrence of multiple allelism. In this post, we will discuss the alleles of the human ABO blood group system and the possible genotypes behind every group of the ABO blood groups.
Alleles and Genotypes for human blood groups – multiple allelism in ABO
An example of multiple allele inheritance occurs in the inheritance of the ABO blood groups of human beings. This is an interesting example as it also involves codominance. In the ABO blood grouping system, there are four blood groups, determined by the presence or absence of two antigens (A and B) on the surface of the red blood cells (figure 1).
Alleles in ABO blood group – multiple Allelism
There are three alleles involved in the inheritance of these blood groups: IA, IB, i
• IA, which determines the production of the A antigen
• IB, which determines the production of the B antigen
• i, which determines that neither antigen is produced
Alleles IA and IB are codominant, but allele i is recessive to both.
genotypes and phenotypes (in ABO blood groups)
The possible genotypes and phenotypes (blood groups) are shown below.
|IA IA, IA i||A group|
|IB IB, IB i||B group|
|IA IB||AB group|
|i i||O group|
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