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How to Determine Your Blood Type Using Just Pen & Paper (Experiment for 13-Year-Olds!)

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Your blood contains vital information, and everyone should know a thing or two about blood, and their blood type when the time comes. 

Welcome to STEM Geek!
Welcome to STEM Geek!

But it’s not just about blood transfusions and donations. By learning how to figure out their blood type using just pen and paper, middle-schoolers can also practice math and probability!

But before we dive into the calculations, let’s learn a bit of context.

Related Post: 3 DNA Science Fair Project Ideas (Extract DNA From Plants & Humans!)

How Does Blood Work?

Blood is a dense, viscose, and red-colored connective tissue that circulates in the organism and delivers vital supplements to every part of the body.

3 Main Functions of Blood


  • It transports Oxygen from the lungs to every living cell and returns Carbon Dioxide from the cells to the lungs.
  • It delivers nutrients, absorbed in the small intestine, to every living cell in the body.
  • It transmits products from different cells to other systems in the body. For example, blood transmits extra water, and electrolytes to the kidneys, and furthermore they are expelled through the digestive tract.
  • It transports hormones produced in the endocrine glands to different organs and cells.


  1. Blood helps with regulating the pH balance in the body.
  2. It regulates the water levels in the body.
  3. It helps the body to maintain its temperature.


  1. Blood contains cells that fight against pathogen microorganisms and different diseases.
  2. Blood contains coagulants, which protect the body from losing blood.

Blood consists of 45% of blood cells and 55% of blood plasma. Which have different forms, and different purposes.

3 Main Types of Blood Cells

Red And White Blood Cells

Red Cells (A.K.A. Erythrocytes)

These contain hemoglobin which gives blood its significant red color. Red blood cells do not have a nucleus.

Function: because they have hemoglobin, they are capable of bonding with Oxygen, Carbon Dioxide, and Carbon Monoxide.

Number of red blood cells per cubic millimeter: 4-6 million/mm³

White Cells (A.K.A. Leukocytes)

Under a microscope, their nucleus absorbs the stains, and the cytoplasm stays transparent and that’s why they are called white blood cells. When complications occur in the body, they are capable of changing their shape.

Function: they are part of the immune system, and they protect the body from infections, and diseases;

Number of white blood cells per cubic millimeter: 6-8000/mm³

Platelets (A.K.A. Thrombocytes)

Platelets are made in the bone marrow, and they have a lifespan of 10 days.

Function: They prevent bleeding, stop bleeding and coagulate blood when needed.

An increased number of thrombocytes indicates that there is an open wound somewhere on the body.

Number of platelets per cubic millimeter: 150-330 000/mm³

Overall, blood holds the body in place, and it’s considered to be the most important liquid in the human body.

Blood types, the number of blood cells, and the Rh factor are genetically inherited. And it’s important to know your family tree and their blood types.

So before we pile up more information, it’s crucial to ask yourself about blood types and what’s their importance.

The Importance of Knowing Your Blood Type

Blood Type Testing

Do you know your own blood type?

It’s very interesting to know how exactly blood groups are inherited.

How Is Blood Hereditary?

We, humans, are a creation of our parents’ genes and alleles. We have 46 chromosomes in our DNA – 23 inherited from one parent, and 23 inherited from the other parent.

Allele From Parents

Chromosomes contain alleles in their structure. Alleles can be a simple base or a specific sequence present in the chromosomes, and it is considered to be a variation of a gene.

The alleles we inherit from our parents can be dominant or recessive.

Dominant alleles are easier to inherit because they overrule any other (recessive) alleles.

For example, if one of your parents has brown or black hair, the chances of you having brown/black hair are more significant than you having light blonde hair. And it all depends on alleles!

The same goes with blood types. Some blood types are more dominant than others. 

Dominant blood genes are type-A and type-B, while type-O is recessive.

There are 4 blood types (groups): A, B, AB, and O. And they are all part of the ABO system used today!

Blood types are determined by the antigens present in the red blood cells. Blood type-A has A antigens, type B has B antigens, type O has no antigens, and type AB has both A antigens and B antigens.

Without knowing the specific alleles present in our parents’ blood types we can create a picture of all the possible outcomes and blood types without knowing the alleles we inherited:

Parent GenesABABO
AA or OA, B, AB, or OA, B, or ABA or O
BA, B, AB, or OB or OA, B, or ABB or O
ABA, B, or ABA, B, or ABA, B, or ABA or B
OA or OB or OA or BO

Blood Transfusions – Who Can Donate to Whom?

Blood Donation

When it comes to donating blood and receiving blood, many things are different from the overall look on blood types and their antigens/ antibodies.

Different blood groups contain different antibodies, type-A contains Beta antibodies (B) thus the individuals who have type-A blood aren’t able to receive type-B blood.

Type-B contains Alpha-antibodies(A), thus the individuals who have type-B blood aren’t able to receive type-A blood.

Type-AB doesn’t contain antibodies, so people with type-AB blood can receive any blood group.

Type-O contains both Alpha and Beta antibodies, so individuals who have type-O blood aren’t able to receive both type-A, type-B, and type-AB blood.

Type-O is considered to be a universal blood type, any blood group can receive type-O blood without any complications.

Ph Factor

Each of these groups can be Rh positive or Rh negative. And that leaves us with 8 blood types in total.

The Rh factor is determined by a rhesus protein which is present in some red blood cells.

Individuals who don’t have the rhesus protein present in their red blood cells are considered to have a negative Rh factor.

Just like blood types, the Rhesus protein is considered to be genetically inherited!

The Rhesus protein is very important for mothers-to-be. If they have any blood type that’s Rh-Negative, and they conceive a child that’s Rh-Positive, the mother’s body will see the child as a foreign substance. So Rh-Negative mothers need to be injected with an RHoGram injection that will stop further complications.

The Rh factor cannot be determined with pen and paper. How so? Because even tho it’s hereditary, you still need to undergo some blood tests to be 100% sure about your Rh factor.

Rh FactorRh-Positive (Rh+)Rh-Negative (Rh-)
Rh-Positive (Rh+)Rh+, Rh-Rh+, Rh-
Rh-Negative (Rh-)Rh+, Rh-Rh-

The dominance of the Rh factor depends on the 2 alleles, and to calculate it at home you need to know both alleles: D – dominant determinant, d – recessive determinant.

Calculate Your Blood Type Experiment

With a little bit of math… Don’t worry, I know how you feel about extra math. But, I promise it’s not complicated!

So, with a little bit of math, you will be able to determine every possible outcome when combining 2 blood groups and Rh factors!

Materials needed:

  • Paper,
  • Pen.


  1. Ask your parents about their blood types, and Rh factor and write them on a piece of paper.
  2. Calculate the possible outcomes of the blood groups, and the Rh factor with the equation below.
  3. After calculating everything you can merge the results of the blood types with the Rh factor, which will give you all the possible outcomes.
Rh Factor

If you don’t want to bother with math and probabilities, you can use the tables below to find the possible outcomes of the two blood types you wrote down.

And if you want to know the possibilities and chances of each blood type, you can search for an online blood type calculator.

If you already know how to calculate blood types, you can try this experiment with peas, and the procedure is the same!

You can also expand the experiment by calculating blood types within generations and you can create a family tree with blood types.

You can even try to experiment and merge your blood type with another blood type to see the possible blood types of your future offspring.

Possible Outcomes in Blood Types

Both parents have blood type A

how to calculate your blood type - chart 1

Both parents have blood type B

Chart 2

One parent has type-A, one parent has type-B

Chart 3

One parent has type-A, one parent has type-O

Chart 4

One parent has type-B, one parent has type-O

Chart 5

One parent has type-A, one parent has type-AB

Chart 6

One parent has type-B, one parent has type-AB

Chart 7

Both parents have type-AB

Chart 8

Both parents have type-O

Chart 9

One parent has type-O, one parent has type-AB

Chart 10

Possible Outcomes in Rh Factor

Both parents are Rh-Positive

Chart 11

One parent is Rh-positive, one parent is Rh-negative

Chart 12

Both parents are Rh-negative

Chart 13

Frequently Asked Questions

What determines the Rh factor?

The Rh factor is determined by the presence of the Rhesus protein in the walls of red blood cells.

If a red blood cell contains the Rhesus protein, the Rh factor is considered to be positive (Rh+).

If no presence is detected, then, the Rh factor is considered to be negative (Rh-).

Which blood types are dominant?

The ABO system used nowadays contains 2 dominant blood types: Type-A and Type-B, while type-O is recessive.

Type-A, and Type-B alleles will overpower any other recessive alleles, thus becoming the dominant blood type in offspring.

What blood type is the universal recipient?

Type-AB Positive is considered to be a universal recipient because AB Positive individuals are able to receive blood cells from every type of blood, even if the blood they receive is Rh-Negative.

Type-AB Positive doesn’t contain any antibodies, thus it is able to merge with any given blood type.

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