Which Parent Determines Blood Type: The Genetics of Blood Typing

Blood type is an essential factor in our health care system. It is necessary to determine a patient’s blood type to apply the correct treatment in case of an emergency. In this article, we’ll explore the genetics behind blood typing and answer some of the most common questions related to the topic.

Blood Typing Basics

Before we dive into the genetics, let’s briefly discuss the blood typing basics:

  • There are four main blood types: A, B, AB, and O.
  • Blood type is determined by the presence or absence of specific antigens on the surface of red blood cells.
  • The presence of an antigen makes a blood type positive (+), while the absence of an antigen makes it negative (-).
  • The Rh factor is another antigen that is either present (+) or absent (-) in blood. A person is either Rh positive or Rh negative.

Genetics of Blood Typing

Now let’s explore how genetics determine blood type:

Multiple Alleles

The genes responsible for determining blood type have multiple alleles. An allele is a variant form of a gene that codes for different variations of a specific trait. In the case of blood typing, there are three alleles: A, B, and O.

A person inherits two copies of each gene, one from each parent. Therefore, an individual can either have two copies of the same allele (homozygous) or one copy of each allele (heterozygous).

Genetic Makeup Blood Type
AA or AO A
BB or BO B

The A and B alleles are both dominant, meaning that if they are present, their blood type will be expressed. The O allele is recessive, meaning that it will only be expressed if a person has two copies of it.

Rh Factor Inheritance

The Rh factor is inherited separately from the ABO blood groups. It is determined by the presence or absence of the Rhesus D (RhD) antigen on red blood cells. Rh positive means that the RhD antigen is present, while Rh negative means that it is absent.

The inheritance of the Rh factor is a classic example of dominant-recessive inheritance. If a person is Rh positive, they can either be homozygous (DD) or heterozygous (Dd). If a person is Rh negative, they are homozygous recessive (dd).

Which Parent Determines Blood Type?

The determination of blood type is not straightforward as it depends on the inheritance pattern of the ABO and Rh genes. However, we can make some generalizations:

  • If both parents have type A blood, their child can either be type A or type O.
  • If both parents have type B blood, their child can either be type B or type O.
  • If both parents have type AB blood, their child will be type AB.
  • If both parents have type O blood, their child will be type O.
  • The Rh factor follows a similar inheritance pattern, but it is not strictly related to ABO blood type.

It is important to note that these are generalizations and not definitive rules. Due to the inheritance pattern of multiple alleles, some blood types may skip generations or appear unexpectedly with certain family combinations.

Why is Blood Type Important?

Blood type is an essential factor in medical treatment, specifically blood transfusions and organ transplants. If the patient receives the wrong blood type during a transfusion, it can trigger an immune response, leading to severe complications and even death.

Therefore, it is crucial that a patient’s blood type is determined before undergoing any medical procedure that involves the transfer of blood or tissue.

Blood Type Compatibility

In blood transfusions, only compatible blood types can be given to the patient. The table below shows blood type compatibility:

A Yes No Yes No
B No Yes Yes No
AB Yes Yes Yes No
O No No No Yes

In general, type O blood is considered the universal donor as it can be transferred to people with any blood type. On the other hand, type AB blood is considered the universal recipient as they can receive blood from any blood type.


Q: Can a blood type change?

A: No, a person’s blood type is determined by their genetics and cannot be changed.

Q: Can two parents with type O blood have a child with AB blood?

A: No, it is not possible for two parents with type O blood to have a child with AB blood as they do not carry the A or B alleles necessary to form the AB blood group.

Q: Is the Rh factor more important than the ABO blood groups?

A: Both the ABO blood groups and the Rh factor are equally essential in determining blood type compatibility, and both must be taken into consideration during medical procedures.

Q: Can blood type affect fertility?

A: There is no scientific evidence to suggest that blood type affects fertility.

Q: Is blood type related to personality traits?

A: No, there is no scientific basis for the belief that blood type is related to personality traits.


Understanding the genetics behind blood typing is essential for our health care system. With this knowledge, medical professionals can determine the correct treatment for their patients and avoid severe complications during medical procedures.


  • https://www.redcrossblood.org/donate-blood/blood-types.html
  • https://www.ncbi.nlm.nih.gov/books/NBK2264/
  • https://www.mountsinai.org/health-library/tests/blood-type-test

Leave a Reply

Your email address will not be published. Required fields are marked *