Blood type is primarily controlled by genetics, specifically the ABO gene inherited from both parents.
The Role of the ABO Gene
The ABO blood type system is determined by a single gene, known as the ABO gene, located on chromosome 9. This gene has three main alleles (versions of a gene):
- IA: This allele leads to the production of the A antigen on the surface of red blood cells.
- IB: This allele leads to the production of the B antigen on the surface of red blood cells.
- i: This allele is recessive and doesn't lead to the production of either A or B antigens.
Inheritance of Blood Types
Each person inherits two ABO gene alleles, one from each parent. The combination of these alleles determines their blood type:
| Genotype | Blood Type (Phenotype) |
|---|---|
| IAIA | A |
| IAi | A |
| IBIB | B |
| IBi | B |
| IAIB | AB |
| ii | O |
- Blood Type A: Individuals with the genotypes IAIA or IAi have type A blood. Their red blood cells have A antigens on their surface.
- Blood Type B: Individuals with the genotypes IBIB or IBi have type B blood. Their red blood cells have B antigens on their surface.
- Blood Type AB: Individuals with the genotype IAIB have type AB blood. Their red blood cells have both A and B antigens on their surface.
- Blood Type O: Individuals with the genotype ii have type O blood. Their red blood cells have neither A nor B antigens on their surface. Because "i" is recessive, a person must inherit two copies to have type O blood.
The Rh Factor
In addition to the ABO blood group system, the Rh factor (Rhesus factor) is another important blood group system. It is determined by the presence or absence of the RhD antigen on red blood cells. Individuals who have the RhD antigen are Rh-positive (Rh+), while those who lack it are Rh-negative (Rh-). The Rh factor is also genetically determined and inherited from parents.
Conclusion
In summary, blood type is determined by the inheritance of specific genes, primarily the ABO gene, from both parents. The alleles present in these genes dictate which antigens are present on the surface of red blood cells, thus determining an individual's blood type. The Rh factor is inherited independently but contributes to a person's complete blood type classification.
