Human blood types exhibit a codominance inheritance pattern, which is a type of inheritance where both alleles in a genotype contribute to the phenotype. The ABO blood group system is determined by the presence of A and B antigens on the surface of red blood cells.
There are three alleles involved in determining the blood type:
- A (IA) - produces A antigens
- B (IB) - produces B antigens
- O (i) - no A or B antigens
The possible genotypes and their corresponding phenotypes for blood types are as follows:
- Type A: Genotypes can be IAIA or IAi
- Type B: Genotypes can be IBIB or IBi
- Type AB: Genotype is IAIB (both A and B alleles are expressed, showing codominance)
- Type O: Genotype is ii (no A or B antigens)
When two parents with different blood types have children, the possible blood types of the offspring can be predicted using a Punnett square. The inheritance of blood type is an example of multiple alleles (more than two forms of a gene) and illustrates how different combinations can lead to different phenotypes in the offspring.