Human Blood Group Inheritance

Human blood type is determined by the presence or absence of specific antigens on the surface of red blood cells. These antigens are inherited genetically, with the ABO and Rh systems being the most clinically significant.

The ABO Blood Group System

The ABO system is determined by three alleles: A, B, and O. Alleles A and B are codominant, meaning both are expressed if present. The O allele is recessive, requiring two copies to produce the O blood type. Possible genotypes and corresponding phenotypes are:

• AA or AO: Blood type A
• BB or BO: Blood type B
• AB: Blood type AB
• OO: Blood type O

The Rh Blood Group System

The Rh system is simpler, with the presence of the Rh D antigen resulting in an Rh-positive (Rh+) blood type and its absence resulting in an Rh-negative (Rh-) blood type. The Rh+ allele (D) is dominant over the Rh- allele (d).

• DD or Dd: Rh+
• dd: Rh-

Inheritance of Blood Type

Each parent contributes one allele for both the ABO and Rh systems. The combination of these alleles determines the offspring's blood type. For example, a parent with genotype AO and Rh+ (Dd) can pass on either A or O for the ABO system and either D or d for the Rh system.

Determining Blood Type

Blood typing is performed through serological tests which identify the presence or absence of A, B, and Rh D antigens on red blood cells using specific antibodies. This process determines the ABO and Rh blood type phenotypes.

Genetic Variations and Rare Blood Types

Beyond the common ABO and Rh systems, numerous other blood group systems exist, each with its own set of antigens and alleles. These less common systems contribute to the vast genetic diversity of human blood types and can influence compatibility in transfusions.