How does AB blood type occur?

The AB blood type occurs when an individual has inherited the A allele from one parent and the B allele from the other parent. This results in the presence of both A and B antigens on the surface of red blood cells, along with the absence of anti-A and anti-B antibodies in the plasma.

The inheritance of blood type is determined by the ABO gene, which has three possible alleles: A, B, and O. Each individual inherits one ABO allele from each parent. The following combinations of alleles result in different blood types:

- AA or AO: A blood type

- BB or BO: B blood type

- AB: AB blood type

- OO: O blood type

In the case of AB blood type, a parent with A blood type (either AA or AO genotype) contributes the A allele, while a parent with B blood type (either BB or BO genotype) contributes the B allele. The offspring inherits both the A and B alleles, resulting in AB blood type.