Blood Group Inheritance Chart (ABO + Rh Factor)
ABO Blood Group Inheritance
| Parents’ Blood Groups | Possible Child Blood Groups |
|---|---|
| O + O | O only |
| 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 (not O) |
Explanation of Inheritance
ABO system: Blood groups are A, B, AB, or O depending on which antigens are present on red blood cells.
Genes: Each person has two ABO genes (one from each parent). Possible alleles are A, B, O.
- A + A or A + O → Blood group A
- B + B or B + O → Blood group B
- A + B → Blood group AB
- O + O → Blood group O
Rh Factor Inheritance
The Rh factor in a child’s blood group is determined by genes inherited from the parents, just like the ABO blood group system.
Here’s the breakdown
- What is Rh factor?
- The Rh factor is a protein (the D antigen) present on the surface of red blood cells.
- If the protein is present → Rh positive (Rh⁺).
- If the protein is absent → Rh negative (Rh⁻).
- Genetics of Rh factor
- The Rh factor is inherited from both parents.
- It is controlled mainly by the RHD gene:
- D (dominant allele) → produces Rh⁺.
- d (recessive allele) → produces Rh⁻ (absence of the D antigen).
- Therefore:
- If a child inherits at least one D allele → child is Rh⁺.
- If a child inherits two d alleles (dd) → child is Rh⁻.
- Possible parental combinations
| Parent 1’s Rh | Parent 2’s Rh | Child’s Rh possibilities |
|---|---|---|
| Rh⁺ (DD) | Rh⁺ (DD) | 100% Rh⁺ |
| Rh⁺ (DD) | Rh⁻ (dd) | 100% Rh⁺ |
| Rh⁻ (dd) | Rh⁺ (DD) | 100% Rh⁺ |
| Rh⁺ (Dd) | Rh⁻ (dd) | 50% Rh⁺, 50% Rh⁻ |
| Rh⁺ (Dd) | Rh⁺ (Dd) | 75% Rh⁺, 25% Rh⁻ |
| Rh⁻ (dd) | Rh⁻ (dd) | 100% Rh⁻ |
In short
- Rh⁺ is dominant over Rh⁻.
- A child will be Rh⁻ only if both parents pass the Rh⁻ gene.