Understanding Blood Type Inheritance
Blood type is determined by genes inherited from both parents. The ABO blood group system involves three alleles: A, B, and O. The A and B alleles are co-dominant, while O is recessive. The Rh factor (positive or negative) is determined by a separate gene.
ABO Blood Group Genetics
Alleles and Genotypes
- Type A: Can have genotype AA or AO
- Type B: Can have genotype BB or BO
- Type AB: Has genotype AB (co-dominant expression)
- Type O: Has genotype OO (recessive)
Inheritance Patterns
| Parent 1 | Parent 2 | Possible Child Types |
|---|---|---|
| O | O | O |
| O | A | O, A |
| O | B | O, B |
| O | AB | A, B |
| A | A | O, A |
| A | B | O, A, B, AB |
| A | AB | A, B, AB |
| B | B | O, B |
| B | AB | A, B, AB |
| AB | AB | A, B, AB |
Rh Factor Inheritance
The Rh factor is determined by the presence (+) or absence (-) of the D antigen:
- Rh Positive (+): Can have genotype DD or Dd
- Rh Negative (-): Has genotype dd (recessive)
Two Rh-positive parents can have an Rh-negative child if both carry the recessive d allele (Dd x Dd).
Clinical Significance
Blood Transfusions
Matching blood types is critical for safe transfusions. Incompatible blood can trigger life-threatening reactions.
Pregnancy Considerations
Rh incompatibility between mother and fetus can cause hemolytic disease of the newborn (HDN). Rh-negative mothers carrying Rh-positive babies may need RhoGAM injections to prevent complications.
Universal Donors and Recipients
- Universal Donor: O- (can donate red blood cells to anyone)
- Universal Recipient: AB+ (can receive red blood cells from anyone)
Blood Type Distribution
Approximate distribution in the US population:
- O+: 37%
- A+: 36%
- B+: 8%
- AB+: 3%
- O-: 7%
- A-: 6%
- B-: 2%
- AB-: 1%
Medical Disclaimer
This calculator provides theoretical probabilities based on Mendelian genetics. Actual blood type inheritance can be affected by rare genetic variants. Blood type should always be confirmed through laboratory testing. This tool is for educational purposes only and should not be used for medical decisions, paternity testing, or legal purposes.