Blood type is an inherited trait that is passed down from parents to their children. The blood type a child has is determined by the blood types of the parents. This is because blood type is controlled by genes. Specifically, there are two genes that determine someone’s blood type – the A gene and B gene. Depending on which genes a person inherits from their parents, this determines whether they have blood type A, B, AB or O. So whose blood type is a child most likely to carry – their mother’s or their father’s? Let’s take a deeper look at how blood types are inherited to understand more.
Blood Type Basics
First, it’s helpful to understand some blood type basics. There are four main blood types:
- Blood Type A – has the A antigen on red blood cells
- Blood Type B – has the B antigen on red blood cells
- Blood Type AB – has both A and B antigens on red blood cells
- Blood Type O – has neither A nor B antigens on red blood cells
Whether you have the A antigen, B antigen, both or neither is determined by the A and B genes. If you inherit an A gene, you will have the A antigen. If you inherit a B gene, you will have the B antigen. If you inherit both A and B genes, you will have both antigens. And if you inherit neither, you will have blood type O.
Now let’s look at how these genes are inherited from parents:
Blood Type Genes
The gene for blood type A and the gene for blood type B are inherited separately from each other, one from each parent. These genes have a dominant-recessive relationship:
- The A gene is dominant over the O gene
- The B gene is dominant over the O gene
This means:
- If you inherit an A gene, you will have the Type A antigen, even if the other gene is O.
- If you inherit a B gene, you will have the Type B antigen, even if the other gene is O.
So what happens if you inherit an A gene from one parent and a B gene from the other? Then you will have AB blood type, since both antigens will be expressed.
The O gene is recessive. So someone will only have blood type O if they inherit O genes from both parents.
How Blood Type is Inherited
Now that we understand the basics, let’s look at how a child’s blood type is inherited from their parents:
If One Parent is Type O
If one parent has blood type O, they can only pass on the O gene to their child, since type O individuals do not have any A or B genes. So the child’s blood type will be determined entirely by the gene inherited from the other parent.
For example:
- If the other parent is type A, the child will be type A.
- If the other parent is type B, the child will be type B.
- If the other parent is type AB, the child will be type A or B, depending on which gene is passed down.
This is summarized in the table below:
| Parent 1 Blood Type | Parent 2 Blood Type | Possible Blood Types for Child |
|---|---|---|
| O | A | A |
| O | B | B |
| O | AB | A or B |
If Neither Parent is Type O
If neither parent has type O blood, the child’s blood type is determined by which genes are inherited from each parent. For example:
- An A parent and a B parent could have a child that is A, B, or AB.
- Two A parents can only have a child that is type A or O.
- Two B parents can only have a child that is type B or O.
- An AB parent and a B parent could have a child that is A, B or AB.
This is summarized in the table below:
| Parent 1 Blood Type | Parent 2 Blood Type | Possible Blood Types for Child |
|---|---|---|
| A | A | A or O |
| B | B | B or O |
| A | B | A, B, AB or O |
| AB | A | A, B or AB |
| AB | B | A, B or AB |
If One Parent is AB
If one parent is AB blood type, they have both A and B genes and can pass on either one. Their child’s blood type will depend on which gene is inherited from the AB parent and the other parent’s blood type. For example:
- An AB parent and an A parent could have a child that is A, B or AB.
- An AB parent and B parent could have a child that is A, B or AB.
- An AB parent and O parent can have a child that is A, B or AB.
This is summarized below:
| Parent 1 Blood Type | Parent 2 Blood Type | Possible Blood Types for Child |
|---|---|---|
| AB | A | A, B or AB |
| AB | B | A, B or AB |
| AB | O | A, B or AB |
Maternal vs. Paternal Blood Types
Based on the inheritance patterns above, we can see that a child’s blood type is equally likely to be the same as the mother’s or the father’s – it all depends on which genes are inherited.
For example, if the mother is blood type A and the father is blood type B, the child could end up with blood type A or B. There is no dominance between maternal or paternal blood types.
Some key points:
- A child can have the same blood type as their mother, father, both or neither.
- Blood type O parents can only have children with blood type O or their spouse’s blood type.
- Two type O parents will always have children with blood type O.
- Blood type AB parents can have children of any blood type.
- There’s no way to predict with certainty which parent’s blood type will be inherited.
So in summary, a child’s blood type is randomly based on which two genes are inherited – one from each parent. All blood types have an equal chance of being passed down.
Rh Factor
In addition to the A and B antigens, blood types are also classified based on the Rh factor. This refers to the Rh(D) protein on the surface of red blood cells. If your blood has this protein, you are Rh positive. If your blood lacks this protein, you are Rh negative.
The Rh factor is also inherited from your parents but works a bit differently than the A/B antigens:
- Most people are Rh positive – about 85% of the population.
- Rh positive is dominant over Rh negative.
- If you inherit one Rh positive gene, you will be Rh positive.
- You need to inherit two Rh negative genes to be Rh negative.
Some key inheritance patterns:
- Two Rh negative parents will always have Rh negative children.
- An Rh negative parent and Rh positive parent have a 50/50 chance of having a child of either blood type.
- Two Rh positive parents will almost always have Rh positive children.
So again, the Rh factor is inherited independently from the A/B antigens. A child could end up with the same Rh factor as their mother, father, both or neither.
Rare Blood Types
While types O, A, B, and AB are the most common, there are also rare blood types that arise from unusual genetic inheritance. Here are a few examples:
Bombay Phenotype (Oh)
This very rare blood type results when a person inherits two non-functional versions of the H gene, which determines the expression of the A and B antigens. Since the antigens are not expressed, the red blood cells look like type O, but it is Oh.
cis AB
This blood type occurs when the A and B genes are inherited together from one parent, rather than separately from each parent. Red blood cells will appear AB, but it differs genetically.
Rh-deficiency
When both parents pass on non-functional Rh genes, the child will be entirely Rh-deficient. This is very rare.
While these blood types are quite uncommon, they illustrate the complexity of blood type genetics. There are many possible combinations that give rise to blood diversity in humans.
Testing Blood Types
Blood typing simply involves testing blood samples for the presence or absence of antigens and proteins to predict a person’s blood type. Some methods include:
ABO/Rh Typing
This test uses antibodies to detect whether blood cells have the A, B, and Rh(D) antigens. The results indicate A, B, AB, or O groups and positive or negative Rh factor.
Reverse Typing
This test uses known A and B antibodies against the blood sample. Agglutination reactions determine compatibility with the antibodies and predict blood type.
Molecular Testing
DNA extracted from blood can be used to test for variants in the ABO gene and Rh genes and predict blood type.
Parents can opt to have fetal blood typing through amniocentesis or chorionic villus sampling. Otherwise, newborns are tested at birth through umbilical cord blood or a heel prick sample.
Knowing a child’s blood type at birth is important in case they ever need a transfusion. Healthcare providers can ensure they receive compatible blood.
Blood Type Compatibility
Blood types must be matched between donors and recipients for safe blood transfusions. Here is how the blood types compare:
| Blood Type | Can Receive Blood From | Can Donate Blood To |
|---|---|---|
| A | A, O | A, AB |
| B | B, O | B, AB |
| AB | A, B, O, AB | AB |
| O | O | A, B, O, AB |
Type O-negative blood is the universal donor, while AB-positive is the universal recipient. But whenever possible, doctors give red cell transfusions that directly match the recipient’s blood type.
The Importance of Blood Types
Understanding blood type genetics and inheritance patterns enables:
- Predicting a child’s blood type from their parents’ blood types
- Testing for rare blood disorders
- Typing and matching blood between donors and recipients
- Linking blood types to disease risk
- Tracing family ancestry and history through bloodlines
While blood transfusions are the most vital use, research continues to uncover new ways that blood type may impact human health and genetics.
Conclusion
In summary, a child’s blood type is determined by the blood type genes they inherit from their biological parents. Each parent passes down one of two genes that encode the ABO antigens and Rh factor. Depending on the specific genes inherited, a child may have blood type A, B, AB, or O, as well as positive or negative Rh factor. There is an equal chance of the child having either the mother’s or father’s blood type, and their type may even differ from both parents. Understanding the inheritance patterns of these genes allows prediction of blood types for medical and ancestry purposes. Continued research aims to better understand the implications of different blood types for health, compatibility, and genetics.