The ABO blood group system in humans is a perfect example of multiple alleles.
Here's how it works:
* Gene: The blood type is determined by a single gene, known as the ABO gene.
* Alleles: This gene has three different alleles:
* I^A: Produces the A antigen on red blood cells.
* I^B: Produces the B antigen on red blood cells.
* i: Produces neither A nor B antigen.
* Genotypes and Phenotypes: These alleles can combine in different ways to produce four possible blood types (phenotypes):
* 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: ii
Key Points:
* The existence of three or more alleles for a single gene is known as multiple alleles.
* In the ABO blood group, an individual inherits two alleles, one from each parent.
* The combination of these two alleles determines their blood type.
* Codominance: The I^A and I^B alleles are codominant, meaning that both alleles are expressed equally in the heterozygote (AB blood type).
This system demonstrates multiple alleles because there are more than two possible alleles (I^A, I^B, and i) for a single gene (ABO gene).
