Several genes with varying inheritance patterns are involved in determining your blood type. The most significant gene is the ABO gene which determines your ABO blood type.

Like many of your physical characteristics, including your eye color or dominant hand, your blood type depends on your genetics.

Genes you inherit from your biological parents determine your blood type, but the inheritance patterns may not resemble the patterns of other traits or conditions you know.

The International Society of Blood Transfusion recognizes 47 blood group systems, and scientists have identified 52 genes responsible for the various blood types in humans.

Keep reading to learn how your genes influence some of the most important blood type groups and why it matters.

The four main blood groups are the ABO blood groups. The names refer to the types of antigens found on red blood cells (RBCs) and antibodies found in plasma. The four types are:

  • A: has A antigens and anti-B antibodies
  • B: has B antigens and anti-A antibodies
  • AB: has A and B antigens but no antibodies
  • O: has no antigens but both anti-A and anti-B antibodies

The ABO gene on chromosome 9 helps determine which blood type you have. You inherit two copies (alleles) of this gene — one from each parent.

This gene has three possible alleles — A, B, and O. A and B are dominant, while O is recessive. That means that if you have an A or B allele with an O allele, you will express the A or B allele. However, if you have both the A and B alleles, you will express both.

This results in four typical outcomes:

Inherited from parent 1 →
Inherited from parent 2 ↓		ABO
AAABA
BABBB
OABO

Because of the dominant and recessive patterns of the alleles, it’s possible to have many different blood types within the same family.

For example, if one parent had type A blood with A and O alleles and another parent had type B blood with B and O alleles, they could potentially produce four children with four different blood types.

The rare Bombay phenotype

Other rare ABO blood types are possible due to other genetic factors. The most famous of these is the Bombay phenotype, which results from a mutation on chromosome 19. This mutation causes a lack of the H antigen present in other blood types.

Although the Bombay phenotype can look like type O blood, it is distinct. People with the Bombay phenotype can only receive blood from other people with the Bombay phenotype.

The Rhesus (Rh) system is the second most important blood type group because Rh antigens are highly immunogenic. That means they can easily trigger an immune response. This is especially important in blood transfusions and during pregnancy.

Your blood can be either:

  • Rh-positive: having Rh antigens on your RBCs
  • Rh-negative: not having Rh antigens on your RBCs

People who are Rh-positive can receive either kind of blood. However, people who are Rh-negative can only receive Rh-negative blood.

The Rh-positive allele follows an autosomal dominant pattern. That means if you inherit at least one Rh-positive allele from either parent, you will be Rh-positive. You need to inherit two Rh-negative alleles (one from each parent) to be Rh-negative.

The genes responsible for determining your Rh blood type are located on chromosome 1.

The third most immunogenic set of antigens belongs to the Kell blood group. Most people aren’t aware of their Kell blood group, but it can be important for blood transfusions.

Your Kell blood type is determined by the KEL gene on chromosome 7. Much like the Rh antigens, you can be either positive or negative for the antigens.

There are 38 Kell antigens, but the two most significant are K (Kell) and k (Cellano). Like the A and B types in the ABO blood group, K and k are codominant, meaning you can express them both.

Knowing your blood type can be helpful if you ever need to give or receive blood. Certain blood types are incompatible with each other. If you receive an incompatible blood type, your immune system will reject the donor blood, possibly leading to a life threatening situation.

However, hospitals do extensive testing before considering a blood transfusion to ensure a proper blood type match.

It’s especially important for pregnant people to know their blood type. Birthing parents who have blood types that are incompatible with their babies may experience complications, such as hemolytic disease of the fetus and newborn.

Can blood types skip generations?

Yes. Because certain alleles for blood types are recessive, you may inherit a recessive allele that a parent did not express but which they inherited from one of your grandparents. Depending on what other allele you inherit, you may express that allele.

Are certain blood types more common in specific populations?

Yes. Because genetics determine blood type, some blood types are more common in certain ethnicities or races. Older research identified specific variations among blood types across various populations around the world, though there hasn’t been much newer research to confirm whether this data is still accurate.

For example, type O blood was most common in Hispanic, Native American, and Black populations. In some indigenous populations in the Americas and Australia, the prevalence of type O blood is close to 100%.

Type A blood was more common in some parts of Europe, while type B was more prevalent in China and India. Type AB is the rarest of the groups but is most common in Japan, Korea, and some parts of China.

Can a person’s blood type change?

In rare cases, your blood type might change. For example, some people with leukemia experience a temporary blood type change when antigens are no longer expressed on their RBCs while they have cancer.

Another possible situation is a bone marrow transplant, in which the recipient’s blood type may temporarily change to match the donor’s blood type.

Can blood types influence your risk of certain health conditions?

A 2020 study found that people with non-type O blood may be at higher risk of thrombotic events, like blood clots or pulmonary embolism. It also found that people with type A may experience less healthy aging than people with type O. However, more research is necessary.

Your blood type is written in your genetic code from the moment you begin your journey as a single cell. There are several different blood group types, but most people are aware of their ABO and Rh types.

The ABO gene determines your ABO blood type. A and B are codominant alleles, while O is a recessive allele. This leads to four primary blood types. Although the O allele is recessive, O is still the most common blood type.

Your genes also determine whether you are Rh-positive or Rh-negative, with the latter being a recessive trait.

There are several other ways to assess your blood type and several other genes that contribute to it. Talk with a healthcare professional to learn more about what information may be important to you.