ABO Blood Typing and Rh Factor Summary

Blood types are determined by specific proteins or glycoproteins located on the surface of red blood cells, also known as erythrocytes.
Type A: Possesses A proteins and produces B antibodies.
Type B: Possesses B proteins and produces A antibodies.
Type AB: Possesses both A and B proteins and produces no antibodies; known as the universal recipient.
Type O: Possesses no A or B proteins and produces both A and B antibodies; O- is recognized as the universal donor.
There are approximately $30$ other families of blood types in humans beyond the ABO and Rh systems.

Blood type inheritance is characterized by multiple alleles and codominance rather than simple Mendelian genetics.
There are six possible genotypes for the four phenotypes: - Type A: $I^A I^A$ (homozygous) or $I^A i$ (heterozygous). - Type B: $I^B I^B$ (homozygous) or $I^B i$ (heterozygous). - Type AB: $I^A I^B$ (codominant expression of both proteins). - Type O: $ii$ (homozygous recessive; no protein expression).

The Rh factor is an additional protein system named after early studies on the rhesus monkey.
Rh+ is the dominant trait (possessing the protein), while Rh- is recessive.
Rh compatibility is critical during pregnancy: an Rh- mother carrying an Rh+ fetus may develop antibodies during childbirth that can attack the fetus in subsequent pregnancies.
This immune response is typically suppressed by medical intervention during the $28\text{th}$ week of gestation.

O+ and A+ are the most common blood types, each representing approximately $38\%$ of the population.
O- individuals make up $6.6\%$ of the population.
AB- is one of the rarest types, found in less than $1\%$ of the population.
Historical distribution: Type B blood was non-existent in native Australian Aborigines and Native Americans prior to European contact, allowing researchers to trace human ancestry.