Difficulty: Challenger (Level 2)
Does your blood group match what your parents have? If not, don’t worry – how you inherit your blood group is more complicated than it appears.
Two of the most important blood group systems are the ABO system and the Rhesus (Rh) system. Doctors rely on this information to perform safe blood donations. Together, the ABO gene and the Rh gene decide your complete blood group (see graphic).
What is the ABO system?
In the ABO system, your blood group is controlled by the ABO gene, which comes in three different versions, known as alleles: A, B and O.
You inherit one allele from each parent; the pair you receive decides if your blood group is A, B, AB or O.
In the ABO system, the A and B alleles are codominant, which means that if you inherit A from one parent and B from the other, your blood group will be AB.
But the O allele is recessive, meaning you will only be in blood group O if you receive an O allele from both parents. If you receive an O allele along with an A or B allele, your blood group will still be A or B.
While the ABO system determines the letter in your blood group, the positive or negative sign next to it is related to the Rh factor.
What is the Rh system?
Like the ABO system, the Rh system is inherited. The Rh-positive allele (Rh⁺) is dominant, and the Rh-negative allele (Rh⁻) is recessive.
If both parents are Rh‑positive and each carries a hidden Rh-negative allele (genotype: Rh⁺Rh⁻) that is passed to their offspring, they can still have an Rh‑negative child (genotype: Rh⁻Rh⁻).
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