ABO Blood Type Inheritance Chart
Wondering what blood types are possible for your baby? This free ABO blood type chart below uses Mendelian genetics to show every parent combination and which outcomes are realistic.
| Parent A | Parent B | Possible Baby Types | Impossible |
|---|---|---|---|
| A | A | A, O | B, AB |
| A | B | A, B, AB, O | None |
| A | AB | A, B, AB | O |
| A | O | A, O | B, AB |
| B | B | B, O | A, AB |
| B | AB | A, B, AB | O |
| B | O | B, O | A, AB |
| AB | AB | A, B, AB | O |
| AB | O | A, B | AB, O (!) |
| O | O | O | A, B, AB |
Why Two Type A Parents Can Have a Type O Baby
The key is understanding genotypes versus phenotypes. You carry two copies of every gene, one from each parent, but only one typically shows up in your blood type. A parent with Type A blood might carry the genotype AA or AO. If they have AO, the A shows (so they appear Type A), but the O gene is still there, hidden but present.
When both parents carry the O gene and both pass it on, the result is OO, which means Type O blood. Here's the breakdown:
- Type A: Can be AA or AO.
- Type B: Can be BB or BO.
- Type AB: Must be AB (codominant).
- Type O: Must be OO (recessive).
Understanding Rh Blood Type Factor & Pregnancy
Your Rh factor is simple: it's a protein that either shows up (+) or doesn't (-). Rh positive is dominant genetically, meaning Rh positive parents are more common than Rh negative.
Rh Incompatibility Explained
When mom is Rh negative and dad is Rh positive, the baby might inherit the positive type. During pregnancy or delivery, fetal blood can mix with the mother's, and her immune system may attack it. The good news: RhoGAM prevents this.
Rare Blood Type Genetic Exceptions
Our calculator handles the vast majority of cases. But genetics has a few curveballs.
- Bombay Phenotype: An extremely rare genetic quirk where someone appears Type O but carries A or B genes that are "silenced" due to a missing enzyme.
- Cis-AB: A super rare mutation where both A and B genes sit on the same chromosome. An AB parent could pass both to a kid, which is normally impossible.