Codominance II Non-mendelian inheritance

Multiple Allele Traits
The majority of human genes are thought to have more than two normal versions, or alleles. Traits controlled by a single gene with more than two alleles are called multiple allele traits. An example is ABO blood type. Your blood type refers to which of certain proteins called antigens are found on your red blood cells. There are three common alleles for this trait, which are represented by the letters IA, IB, and i.

There are six possible ABO genotypes, because the three alleles, taken two at a time, result in six possible combinations. The IA and IB alleles are dominant to the i allele. As a result, both IAIA and IAi genotypes have the same phenotype, with the A antigen in their blood (type A blood). Similarly, both IBIB and IBi genotypes have the same phenotype, with the B antigen in their blood (type B blood). No antigen is associated with the i allele, so people with the ii genotype have no antigens for ABO blood type in their blood (type O blood).
Codominance
Look at the genotype IAIB in the ABO blood group table. Alleles IA and IB for ABO blood type are neither dominant nor recessive to one another. Instead, they are codominant. Codominance occurs when two alleles for a gene are expressed equally in the phenotype of heterozygotes. In the case of ABO blood type, IAIB heterozygotes have a unique phenotype, with both A and B antigens in their blood (type AB blood).

Видео Codominance II Non-mendelian inheritance канала BioMagica