What are the four human blood types in ABO blood group typing?

The ABO blood group system is the most significant classification for human blood transfusions. It categorizes blood into four major types based on the presence or absence of specific antigens (A and B) on the surface of red blood cells [2]. These four types are A, B, AB, and O [5]. Blood group A has A antigens, group B has B antigens, group AB has both, and group O has neither [4]. While the underlying genetics involve six possible genotypes (such as AO, BO, AA, BB, AB, and OO), the dominance of the A and B alleles over the O allele results in only these four distinct phenotypes or blood types [3]. This system was developed after scientists identified that mixing incompatible blood types causes red blood cells to clump together, which can be life-threatening during medical procedures [2].

Sources

1. [1] https://www.cancer.gov/publications/dictionaries/cancer-terms/def/abo-blood-group-system
2. [2] https://medlineplus.gov/ency/article/003345.htm
3. [5] https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/blood-groups
4. [4] https://www.ncbi.nlm.nih.gov/books/NBK2267/
5. [3] https://www.sciencedirect.com/topics/medicine-and-dentistry/blood-group-rh