Blood Types and Genetics

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Blood Types and Genetics

12-BloodTypes-Genetics.doc Standard 8.0 – RT, RI, Monitoring, Feedback, Mastery © Olympian High School

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Human blood comes in a variety of genetically determined blood groups. Knowing a person’s blood group is critical because using the wrong type of blood for a transfusion during a medical procedure can be fatal. A number of genes are responsible for human blood groups, but the best known are the ABO blood groups and the Rh blood groups.

The Rh blood group is determined by a single gene with two alleles—positive and negative. Rh stands for “rhesus monkey,” the animal in which this factor was discovered. The positive (Rh+) allele is dominant, so persons who are Rh+/Rh+ or Rh+/Rh- are said to be Rh-positive. Individuals with two Rh- alleles are Rh-negative.

The ABO blood group is more complicated. There are three alleles for this gene, IA, IB, and i. Alleles IA and IB are codominant. These alleles produce molecules known as antigens that can be recognized by the immune system on the surface of red blood cells. Individuals with alleles IA and IB produce both antigens, making them blood type AB. The i allele is recessive. Individuals with alleles IAIA or IAi produce only the A antigen, making them blood type A. Those with IBIB or IBi alleles are type B. Those who are homozygous for the i allele (ii) produce no antigen, and are said to have blood type O.

When a medical worker refers to blood groups, he or she usually mentions both groups at the same time. For example, if a patient has AB-negative blood, it means the individual has IA and IB alleles from the ABO gene and the Rh- allele from the Rh gene.

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Blood Groups

Phenotype
(Blood Type) / Genotype / Antigen on Red Blood Cell / Safe Transfusions To / Safe Transfusions From
A / IAIA or IAi / A / A, AB / A, O
B / IBIB or IBi / B / B, AB / B, O
AB / IAIB / A and B / AB / A, B, AB, O
O / ii / none / A, B, AB, O / O