How Common Is it for Siblings to Have the Same Blood Type?

This blog post will answer the question, “How common is it for siblings to have the same blood type? The blog will also cover the introduction to ABO genes, the relationship between genes and proteins, and what makes a blood type positive and negative.  

How Common Is it for Siblings to Have the Same Blood Type?

Although it is not definite that siblings will have the same blood type, there is a high probability that they will. Read on to know more about how two siblings can have the same blood type. Identical twins, on the other hand, will always have the same blood type. Non-identical twins may have different blood groups as long as their parents’ blood type differs. 

Introduction to ABO Genes

Deoxyribonucleic acid or DNA refers to your genetic composition. Genes are DNA segments, and human beings are known to have the same twenty-and-odd thousand genes. The genetic variations are what make us unique. 

For instance, the blood type gene, ABO, is present in all of us. The different blood types occur due to the three variants, or alleles, of these genes, namely, A, B, and O. This blood type gene either codes for A, B, or neither, i.e., O. 

However, things are not so simple. We have 23 pairs of chromosomes, which contain genes and long strands of DNA. Each pair of these chromosomes is inherited from each parent. The blood type chromosome carries one allele of this gene. 

Because these genes are inherited from our parents, there is a possibility of sharing specific traits with them, including blood type. However, it is not definitive. As there are two copies of chromosomes, there are six potential combinations, including:

  • AA
  • AB
  • AO
  • BB
  • BO
  • OO 

These combinations are known as blood type genotypes (i.e., the genetic composition of an individual). This brings us to a question regarding the existence of only four blood groups when we have six possible groupings. 

Relationship between Genes and Proteins

Humans are typically made of proteins, and the DNA, genes, and chromosomes are involved in producing these proteins. While the DNA provides a template to make a specific protein, genes offer detailed information to make the protein, including how much and when to make it. Various genes make various protein versions. 

Therefore, the A variant of the blood type gene makes the A version of a protein, while the B variant makes the B version of the protein. On the other hand, the O variant makes neither version. This is because the A and B are dominant genes, while the O variant is the recessive gene. 

Phenotype refers to the physical composition or the observable characteristics of an individual, and in this case, the blood type. As the O variant implies no protein, our six genotypes can be categorized into four phenotypes.

Phenotype AAABBBO

Despite the six possible genotypes, we have only four phenotypes or blood types: A, AB, B, and O. 

Let us now take an example of a male biological parent with the blood type genotype BO and a female biological parent with AA. You get one allele from each of your birth parents. Let us suppose you get the genotypes BO, and your sibling inherits BB, as illustrated below.

In this case, both of you will have type B blood, although the genetic composition is different. Now let us understand all of the possible offspring blood types in this case.

Allele from the birth fatherAllele from the birth motherOffspring genotype Offspring blood type

This table shows us that there are four possible genotypes and three possible phenotypes for the offspring to inherit. Both you and your sibling might have the same blood type with the same genetic composition or, in the case illustrated above, have the same blood type despite different genetic composition.

Positive or Negative?

You may be wondering that the explanation so far only accounts for the alphabet component of a blood type. What about the positive and negative signs given at the end of a blood type, like A+, O-, and so on. 

The positive or negative blood type is determined by a protein known as the Rhesus (Rh) factor, which is present on the red blood cell’s surface. If the protein is present, you have a positive blood type, and if it is not, you have a negative blood type. 

Just the way one gene determines ABO, one gene determines your Rh factor. To have a positive blood type, you need to inherit at least one copy of the Rh factor from either of your biological parents. For a negative blood type, both the inherited alleles of the Rh gene must be negative.  

In the case illustrated above, let us suppose that the mother’s genotype is Rh+/Rh-, which makes her blood group AB+. If the father has a composition of Rh-/Rh-, his blood group would be B-. if you and your sibling inherit the Rh- allele from each of your parents, both of you will have the blood group B-. 


This blog post answered the question, “How common is it for siblings to have the same blood type?” The article also introduced the concept of ABO genes, the relationship between genes and proteins, and what makes a blood type positive and negative.  

If you’ve enjoyed the How Common Is it for Siblings to Have the Same Blood Type? mentioned above, I would recommend you to take a look at ”How Common Is it for Siblings to Have the Same Birthday?” too.

Frequently Asked Questions (FAQs): How Common Is it for Siblings to Have the Same Blood Type?

Is blood type likely to run in the family?

Our blood type is inherited from our parents just the way other aspects of us are. Each parent passes on one of the two ABO genes. While the A and B alleles are the dominant ones, the O allele is recessive. For instance, if the O allele is combined with A, the blood type will be A because A is dominant.

How is the negative or positive blood type determined?

Rhesus (Rh) factor refers to an inherited protein found on the red blood cell’s surface. The presence of this factor implies that you are Rh-positive, while the lack of it indicates Rh-negative. Everybody has two Rh factors from each of their parents. 

The surefire way of someone having a negative blood type is for both parents to have a minimum of one negative Rh factor. If both of your Rh factors are positive, you can never give birth to a child with a negative blood type. 

Can a man with O+ blood and a woman with A+ blood have a child with O- blood?

Yes, a man with O+ blood and a woman with A+ blood have a baby that has O- blood. It is highly probable that the father has a negative Rh factor in such an occurrence, while the mother has an O allele. 

Both the parents would have passed on their O alleles and a negative Rh factor to their child, resulting in a child with O- blood. There is a 1 in 8 chance of each of their children having this blood type.

Whom are you genetically more similar to, your parent or sibling?

You are genetically equally similar to both our siblings and our children. You share 50% of your DNA with each of your parents. You also share 50% of your genetics with your siblings. The only exception is that of identical twins as they share all of their genetic material. 

The further the degree of genetic closeness, such as extended family members, the less you share your DNA. You share 25% of your DNA with each of your grandparents and your parents’ siblings, while you share 12.5% of your genetics with your first cousins.

Is your blood type related to your health?

Some experts state that even if your blood type is linked to your health, it is of negligible consequence. However, others believe that there is a genuine relationship. 

They claim that the ABO alleles that determine your blood type is not only present on the red blood cells’ surface but also in other bodily tissues, which indicate susceptibility to specific conditions. Here is a list of possible connections between the blood type and your health.

Individuals with A and AB blood type are likely to be most susceptible to gastric cancer;
Individuals with O blood type are at the lowest risk of developing heart diseases while those with A and AB are the most likely; and
Individuals with A blood type find it the most challenging to regulate their stress levels, leading to various stress-related disorders due to excessive cortisol production.

Which blood type do African Americans likely to have?

70% of African Americans are have either the O or B blood. These are the blood types that are of maximum demand, and therefore, their donations in blood camps are crucial. 

Which blood type is associated with longevity?

The type O blood is associated with longevity, as people with this blood type tend to live longer. Such longevity may be linked to a lowered risk of cardiovascular diseases. 

Which is the rarest blood type?

One of the rarest blood types is known as “golden blood,” or Rhnull, and people with this blood type completely lack Rh antigens. An Aboriginal Australian was the first to report such a blood type, and since then, fewer than 50 people are known to have it. Such rarity poses challenges regarding donations when an individual with the Rhnull blood type needs it. 

What do you mean by blood incompatibility?

Blood incompatibility occurs when there is a conflict between the mother’s and her child’s blood types. Such a discrepancy leads to the development of antibodies in the mother’s blood cells that damage the fetus’ blood cells, resulting in jaundice. There is a heightened risk during or around the time of delivery.   

The ABO incompatibility takes place in the following cases.

The mother is of the type B blood, while her baby is A or AB;
The mother’s blood type is O, while that of her baby is A, B, or AB; and

The mother’s blood type is A, while her baby’s blood type is B or AB.
The Rh factor’s incompatibility happens when the mother has Rh-negative blood while the baby’s blood is Rh-positive.


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