Blood type Punnett square
Choose each parent’s genotype, the two gene copies they actually carry, and watch the four possible children fill in.
Result: AB 25%A 25%B 25%O 25%
Combined blood type odds
Putting both squares together (4 × 4 = 16 equally likely outcomes) gives the full blood type for this pair:
| Child | Chance | Out of 16 |
|---|---|---|
| 18.8% | 3 | |
| 18.8% | 3 | |
| 18.8% | 3 | |
| 18.8% | 3 | |
| 6.3% | 1 | |
| 6.3% | 1 | |
| 6.3% | 1 | |
| 6.3% | 1 |
How it works
Each parent has two copies of the ABO gene and passes one, at random, to each child. The square lists both copies from each parent and crosses every pairing, so each box is one equally likely outcome: 1 in 4.
- A and B are co-dominant. An A from one parent and a B from the other makes AB.
- O is recessive. AO looks like type A; only OO gives type O.
- Rh D is dominant. DD and Dd are Rh positive; only dd is Rh negative.
Don’t know your genotype? The blood type calculator works from blood types alone and gives a range.
Blood type genotypes
| Blood group | Possible genotypes | Can pass on |
|---|---|---|
| A | AA or AO | A, or A or O |
| B | BB or BO | B, or B or O |
| AB | AB | A or B |
| O | OO | O |
| Rh positive | DD or Dd | D, or D or d |
| Rh negative | dd | d |
Frequently asked questions
What are the six blood type genotypes?
For ABO there are six genotypes: AA, AO, BB, BO, AB and OO. They produce four blood groups: A (AA or AO), B (BB or BO), AB and O (OO).
How do you do a blood type Punnett square?
Write one parent’s two alleles across the top and the other parent’s two down the side. Fill each of the four boxes with one allele from its column and one from its row. Each box is a 25% chance.
What is the genotype for O negative?
OO for ABO and dd for Rh. Both copies of each gene must be the recessive version.
Is A dominant over B?
No. A and B are co-dominant: when both are present, both antigens are made and the person is type AB. Both A and B are dominant over O.