Here's how it works:
* Gene: The ABO blood group system is determined by a single gene called ABO, located on chromosome 9.
* Alleles: This gene has three common alleles:
* I^A: Codes for the production of the A antigen on red blood cells.
* I^B: Codes for the production of the B antigen on red blood cells.
* i: Codes for the production of neither A nor B antigens.
* Phenotypes: These alleles combine to create four different blood types:
* Type A: I^A I^A or I^A i
* Type B: I^B I^B or I^B i
* Type AB: I^A I^B
* Type O: i i
In summary, a single gene (ABO) with three alleles (I^A, I^B, and i) determines the four different ABO blood types.
