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Blood Types: History, Genetics, and Percentages Around the World

With a degree in biochemistry, Leah works for a small biotechnology company and enjoys writing about science.

Blood Group Picture

Blood type is determined by sugar-based antigens on the red blood cell surface. Those with type O blood do not have any antigens at all.

Blood type is determined by sugar-based antigens on the red blood cell surface. Those with type O blood do not have any antigens at all.

What Is Blood Type?

Red blood cells (called erythrocytes) have a type of antigen on their surface. Composed of sugar molecules, these antigens are called agglutinogens. There are two types of agglutinogens: type A and type B. The type of antigen on the surface of your red blood cells determines your blood type.

There are four basic blood types, made up from combinations of the type A and type B antigens.

Type A: The red blood cells have the type A agglutinogen.

Type B: The red blood cells have the type B agglutinogen.

Type AB: The red blood cells have both type A and type B agglutinogens.

Type O: The red blood cells do not have any agglutinogens at all.

There is another protein (called Rh factor) that is sometimes found on red blood cells. If a person has Rh factor, their blood type is called “Rh positive.” An individual lacking this protein is called “Rh negative.” Combined with the ABO blood types described above, a person may be A+, A-, B+, B-, AB+, AB-, O+, or O-.

Blood Group Poll

Blood Types Around the World

Blood types vary depending on the geographical region: Scandinavians have a high probability of carrying the A blood type, while those indigenous to central Asia are more likely to carry the B blood type. The O blood type is the most common blood type around the world.

According to the National Center for Biotechnology Information (a molecular biology resource funded by the government), the breakdown of blood type by region is:

Blood Type A: Central and Eastern Europe

The A blood group is common in central Europe. Nearly half the population in Denmark, Norway, Austria, and the Ukraine have this blood type. This blood type is also found in high levels among small, unrelated groups of people. In Montana, 80% of the Blackfoot tribe has the A blood group.

Blood Type B: Asia

The B blood type is rare in Europe (about 10% of the population), but fairly common in Asia. Nearly 25% of the Chinese population demonstrates this blood type. This blood type is also fairly common in India and other Central Asian countries.

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Blood Type AB: Asia

The AB blood type is the rarest of all. It is found in up to 10% of the population in Japan, Korea, and China, but is extremely rare in other regions.

Blood Type O: The Americas

The O blood type is the most common around the globe, and is carried by nearly 100% of those living in South America. It is the most common blood type among Australian Aborigines, Celts, those living in Western Europe, and in the United States.

Rh Factor

The majority of people in any geographical region are Rh positive. Caucasians are the most likely to be Rh negative, with approximately 17% of blood donors demonstrating a lack of this protein. Native Americans are the next highest proportion of the population to test as Rh negative: approximately 10% of donors from this population lack this protein.

Coconut Juice Blood Transfusions in World War II

As World War II raged through the Pacific, blood products were in short supply. In emergency situations, Japanese and British medics would resort to coconut water. Coconut water (the juice inside a young coconut, not "milk" which is made from grinding up the meat of the fruit) has fewer electrolytes than blood plasma, but it is sterile and works in a similar manner to a saline IV drip. In a pinch, coconut water is tolerated fairly well by humans. In fact, coconut water preserves teeth better than milk - something to keep in mind the next time a tooth gets accidentally knocked out!

The History of Blood Transfusions

In the 19th century, no one understood that people had different blood types. Blood transfusions often resulted in death, as the receivers immune system would attack the foreign, unmatched blood that was transfused.

The history of blood transfusion goes all the way back to the 1600’s, when William Harvey discovered the circulatory system. By 1658, Jan Swammerdam was viewing red blood cells through a microscope. The very first transfusions occurred in dogs, as the English physician Richard Lower demonstrated that a dog could be kept alive by transfusing blood from other dogs.

Unfortunately, the move to human transfusion was quite tricky. As there was no understanding of blood groups, blood transfusions were extremely risky. Sometimes they were successful: in 1818 James Blundell managed to accomplish the first successful human blood transfusion, and saved a woman hemorrhaging from childbirth. Other people, however, simply went into shock and died after blood transfusions.

Some scientists attempted to prevent the adverse reactions to blood transfusions by transfusing blood substitutes. The transfusion of cow’s milk was attempted in 1854 in Canada, during a cholera epidemic. Drs. Bovell and Edwin Hodder started intravenous transfusions of milk in the belief that the fat molecules in milk could be transformed into white blood cells, and that white blood cells were an immature version of red blood cells. This belief was erroneous, of course, but they had success with one sick man who responded favorably to the transfusions. Two other patients, however, died after milk was transfused into their veins.

These experiments were discontinued in Canada shortly after the cholera epidemic, but were revived in New York City a few years later. Using goat’s milk this time, Dr. Joseph Howe transfused patients suffering from terminal tuberculosis. The patients all demonstrated nystagmus (shaking eye movements) and chest pain, and all of the patients died a few hours after transfusion.

Despite the lack of obvious benefit, milk transfusions continued in the late 1880’s, as the use of blood was discouraged since it had a tendency to coagulate. As more patients died from milk transfusions, the practice fell out of favor. In the 1880’s, isotonic saline solution was invented, and the use of milk fell entirely out of favor in favor of the new, safe saline solution. The revival of blood transfusions would have to wait for the 20th century, when a new era of microbiology ushered in the understanding of various blood groups and compatibility.

In 1901, an Austrian doctor named Karl Landsteiner recognized the three basic blood groups – blood was first cross matched in 1907. Blood storage was still a problem during the early days of blood transfusion – while the compatibility issues had been resolved, blood still had a tendency to clot during storage. Anticoagulants like sodium citrate were developed in the year 1914, allowing blood storage for an extended period of time. The discovery of Rh factor in 1940 allowed doctors to completely understand the compatibility issues among blood donors and recipients, and the American government started its first national blood collection program shortly thereafter.

Blood Typing Video

Blood Type Tests and Blood Transfusions

A traumatic car accident has occurred, and a severely injured patient is rushed to the emergency room. As the patient lies bleeding, doctors scurry to take a sample of the patient’s blood and have it sent away to be typed and cross-matched.

In the laboratory, a technician applies the blood to a special card, which contains antibodies to the A and B blood groups. If the patient’s blood clumps around the A antibody, this means they have the B antigen and it is attacking the A antibody. If the patient’s blood clumps around the B antibody, then the patient has the A blood type. If the patient’s blood clumps around both the A and the B antibody, they have the O blood type, and if the patient’s blood doesn’t react to either the A or B antibodies, then he or she has the AB blood type.

In the case of our patient, the blood clumps around both the A and the B antibodies. The patient has the O blood type. An Rh test is also performed, and our patient is positive for this protein.

As determined by this test, the patient needs a transfusion of type O+ or O- blood. The blood bank releases type O+ blood for use, and the patient is then cross-matched to be sure there are no adverse reactions.

The sample of the O+ blood is taken from the blood bank and mixed with the patient’s blood in a test tube. The sample is watched for any adverse reaction, and if no clumping is noted, the blood is safe for the patient to use. The sample demonstrates no reaction with our patient’s blood, so the bag of donated, O+ blood is rushed down to the waiting patient. As blood is transfused, the patient’s vital signs improve.

Blood Types and Compatibility

The AB+ blood type is known as the Universal Receiver: an individual with this blood type can receive any other blood type without reaction.

The AB- blood type may receive blood types A-, B-, or O-; any transfused blood must be Rh negative to avoid reaction.

The A+ blood type may receive blood types A+, A- , O+, or O-.

The A- blood type may receive blood types A- and O-.

The B+ blood type may receive blood types B+, B-, O+, or O-.

The B- blood type may receive blood types B- or O-.

The O+ blood type may receive blood types O+ or O-.

The O- blood type may only receive the O- blood type. People with O- blood are known as Universal Donors, as their blood will not cause a reaction with any other blood type when donated, since the blood lacks all surface antigens and will not provoke an immune system attack in the receiver.

Blood Compatibility and Rh Factor

Blood Type Complications: Rh Factor in Pregnant Women

For most people, blood type is of little consequence in life. Sometimes, however, a woman is Rh negative and becomes pregnant with a baby who is Rh positive. If this is the first pregnancy, the baby is usually fine because the mother’s blood doesn’t mix with the baby’s during the gestational period. Sometimes, however, the baby’s and mother’s blood mixes during delivery. The mother’s immune system then begins to mount a defense against the foreign protein.

When the mother gets pregnant for the second time with an Rh positive baby, the risks are much higher. In this case, the mother’s immune system may react to the foreign Rh protein carried by the baby. When this happens, the mother’s immune system attacks the baby’s red blood cells, causing them to rupture. The baby develops a form of hemolytic anemia, which can be fatal.

To prevent harm to the baby, the mother can be given injections of Rh immune-globulin. The Rh immune globulin is an antibody for the Rh factor: if any of the baby’s blood has made its way into the mother’s system, the Rh immune-globulin binds to the infant’s blood cells. These “borrowed” antibodies will prevent the mother’s immune system from producing her own.

If a mother demonstrates high levels of Rh antibodies in her blood system, the baby is carefully monitored. If the baby shows signs of distress, a procedure known as an exchange transfusion is sometimes performed to replenish the infant’s blood supply.

Blood Type Inheritance

Inheritance patterns of the ABO blood groups - A and B are codominant, so those who inherit type A and type B alleles will have type AB blood. Those with types AO or BO will be type A or B, respectively.

Inheritance patterns of the ABO blood groups - A and B are codominant, so those who inherit type A and type B alleles will have type AB blood. Those with types AO or BO will be type A or B, respectively.

Blood Type Genetics

Blood types A and B are co-dominant, so if the father has blood type AA and the mother has blood type BB, the child will have a blood type of AB.

Blood Type O is recessive, so a child will only have this blood type if he or she gets two O blood type genes from his or her parents. If both parents are blood type O, all of the children in the family will have the O blood type. Another way this can happen is if the parents are heterozygous for the O allele: this means the mother may be blood type A, but her genotype (the genes she carries) are really AO. In this case, she expresses the A blood antigen, but she also has a gene for the O blood type. If she marries another heterozygote AO carrier, there is a chance that one of their children would inherit both O genes and then have the O blood type. The chance of this family having a child with the O blood type is 25% - there is a 50% chance they would have a child with the AO genotype (which would have the A blood type) and a 25% chance they would have a child with the AA genotype (A blood type).

Blood type A is dominant over blood type O, so anyone who has one A gene will have the A blood type, even if they carry one type O gene.

Blood type B is dominant over blood type O, so anyone who has one B gene will have the B blood type, even if they carry one type O gene.

Rh factor is dominant, so a parents who are have two alleles for Rh factor will have children who are Rh positive. If the parents are heterozygous (having one Rh factor allele and one Rh negative allele), they have a 25% chance of having an Rh negative child. If both parents are Rh negative, all of their children will be Rh negative.

Questions & Answers

Question: What percentage of African Americans have type A blood?

Answer: According to the American Red Cross, approximately 26% of African Americans have type A blood. Of this percentage, 24% are A+ and 2% are A-.

Question: I have type O, RH positive so are my parents the same type?

Answer: Your parents may not have the same blood type you do. The O blood type is double-recessive, so your parents could be type A, type B, or type O and still have a child with an O blood type.

Question: My mum, my sister and myself have A- blood, but my younger sister has AB. What blood type would our father have had?

Answer: Your father likely had Type BO blood. If your mother is type AA and your father is type BO, then the combinations would have resulted in a 50% chance of having type A blood (AO genotype, but O is recessive) and a 50% chance of having type AB blood (the A and B types are co-dominant and will express themselves at the same time).

Question: I recently discovered through our family's research that all of the men on my father's side all had/have O- blood. I'm the son of a genetically identical twin and the other twin had twin boys with O+ blood. First can you explain why all of the men in my lineage have O-blood? And why are my aunt's son O+? My parents were also O-.

Answer: The negative Rh factor is recessive, so it is likely that your mother and father were both negative. Your uncle was an identical twin to your father, which means he was also negative. If your uncle married a woman with a positive factor, then there would be a 50% chance of each child having a positive factor at birth, and a 50% chance of having a negative factor. The positive factor is dominant.

Question: How did I get an AB+ blood type?

Answer: Blood types A and B are co-dominant, so if you inherit the A blood type from one parent and the B blood type from another parent, it is quite possible to have type AB blood. The positive Rh factor is fairly common and is inherited separately from the AB type.

Question: Can a baby get the Rh negative blood type from a grandparent if both parents are positive?

Answer: The Rhesus factor is a recessive trait, so a baby can inherit a negative Rh factor if both parents are positive heterozygotes. In this scenario, we could suppose that a grandparent is Rh negative, but has a husband who is Rh positive. Their child would likely be Rh positive, but would carry the gene for a negative rhesus factor (this is called a heterozygote - they carry the gene but do not express the trait). If this child grew up and married another heterozygote, they would have a 25% probability of having a baby that is Rh negative, a 50% chance of having a child who is Rh positive and a carrier of the negative gene, and a 25% chance of having a child who is positive and does not carry the negative gene at all.

Question: My mom is O positive and my father was A positive, but I'm O negative, how is this possible?

Answer: This would be possible as type O is recessive, along with the negative blood type. In this case, your mother would be O+O- and your father would be A+O-. While they demonstrate only the dominant form of each gene (the positive Rhesus factor for both and the A blood type for your father), each one carries the O- gene and passed it on to you.

Question: My blood type is AO, and my children’s father is type O. How does my son have type AB?

Answer: I cannot explain how your child has type AB blood if his biological father has type O blood. Type O blood is double recessive. With a mother having AO blood and the father having OO blood, the possible combinations are AO, AO, OO, and OO. Your children would have a 50% chance of having type A blood (the AO genetic type) and a 50% chance of having type O blood (the OO genetic type).

Question: What does it mean if my mother is RH- blood type and I'm O- blood type? What does this say about me?

Answer: Your mother's Rh factor is negative, and so is yours! You don't give your mother's blood type, which is typed as a letter (A, AB, B, or O). The O blood type is recessive, so for someone to have the O blood type, they need two recessive "O" genes. Your mother could be A, B, or O since many people who are type A or B carry an O gene (A and B are dominant over O).

Question: I have A+ blood. My father was of Sicilian descent. My mother was of German and Irish descent. Is A+ blood type compatible with my genealogy?

Answer: Yes, the A blood type is compatible with your ancestry. The A blood type is dominant and is found throughout Europe.

Question: My dad is Syrian with type O+ and my mom is African mixed with Indian and carries B+ however my sister and I carry type AB+. How is that possible?

Answer: It would not be theoretically possible for a parents with type O and type B to produce children with type AB blood.

Question: I have AB blood. My father's side all have O blood and my mother's side all have O blood. Is it possible for two type O parents to have a child with blood type AB?

Answer: It is highly unlikely that two parents with Type O blood would produce a child with an AB blood type. Since the O blood type is double recessive, your parents each have OO and OO, which would result in all children having type O blood. To obtain Type AB, one parent must have Type A, B, or AB blood and the other parent must also have type A, B, or AB blood.

Question: In what part of the world is Rh negative blood type most commonly found?

Answer: Australia has the highest percentage of Rh negative blood, with approximately 19% of the population demonstrating a negative factor. The Basque population in Spain has the highest percentage of Rh negative blood as an ethnic group, with 21-43% of Basque people demonstrating the negative factor (dependent on location).

Question: I have blood type B+ but my mother is from Germany. Is my blood type compatible with my genealogy?

Answer: Yes, it is possible to have type B+ blood with German ancestry. There has been a lot of migration and movement throughout human history, and currently 11% of Germans have type B blood (9% have type B+ and 2% have type B-).

Question: If I am AB+ what were my parents?

Answer: Your parents might both be type AB, one parent might be type AB and the other might be type A, one parent might be type AB and the other type B, or you may have one parent that is type A and one parent that is type B. Any of these combinations could produce a child that is type AB.

For the + Rh factor, both of your parents are Rh positive.

Question: What is the most common blood type in Sweden?

Answer: The most common blood type in Sweden is A+. Approximately 37% of the population has this blood type. The second most common blood type in Sweden is O+.

Question: I am an A+ blood type and I want to get married. Which blood group should I marry?

Answer: You should not consider someone else's blood type when you are considering a future spouse. Blood type has no bearing on health or general compatibility.

Question: Why is Africa excluded from your article's world analysis?

Answer: Africa is not excluded from this world analysis. The listing of blood type percentages simply lists the continent where each blood type is the most common. In this synopsis, Type A has the highest prevalence in Europe and Central Europe, Type O has the highest prevalence in the Americas, Type B and Type AB have the highest prevalence in Asia.

Type O+ blood is the most common across the continent of Africa, but it does not have the highest prevalence in the world of this blood type. 45% of South Africans have Type O blood, but this is not the highest prevalence (nearly 100% of South Americans have Type O blood). In short, the blood types across the continent of Africa are varied and it does not have the highest prevalence of any one blood type.

Question: What is the youngest type of blood in humans?

Answer: According to the BBC, type AB is the most recent blood type in humans. While the O blood type is universally compatible, it is not likely to be the oldest blood type among humans. Both the A and B types may become O with a few mutations, so it is likely that A is the oldest, followed by O or B. There are competing theories on blood type and evolution. Each type varies by geographical region and ethnicity.

Question: My mom, dad, and sister have type O negative blood, but I have a positive Rh factor., is this possible?

Answer: In general, the negative Rh factor is a double recessive gene. If both of your biological parents are Rh-negative, then you should also have a negative Rh factor.

Question: You said blood type A is dominant over O. I'm A- and my son is O+. I don't know what blood type his dad is, though. Do you know if my son is recessive rh-? Does this mean I am recessive rh+?

Answer: The positive Rh trait is always dominant. Since you are A-, that means you have two Rh negative alleles. Your son's father is most likely type O+ blood. You carry an O allele (so your genotype would be A- O-). In your case, the O is recessive and so you only display the physical characteristic of the A blood type. Your son inherited one copy of the O gene from you and from his father. He inherited one negative Rh factor gene from you and one positive Rh factor from his father, so he displays the Rh positive phenotype (since the positive gene is dominant).

Question: Can an A- person ever have 2 parents each with O+ blood type?

Answer: A person may inherit a negative Rh factor from two parents with a positive factor, if each parent is heterozygous for this trait. If the mother is +/- and the father is +/-, each will have a phenotype (physical characteristic) of having a positive Rh factor while still carrying the negative Rh factor gene. Each child would have a 25% chance of inheriting both Rh - alleles and demonstrating that phenotype. Two parents with type O blood, however, would not have a biological child with type A blood. Type O blood is double recessive.

Question: What percentage of African Americans have type B blood?

Answer: 18% of African Americans have type B+ blood, and 1% have B-. Excluding Rh factor, 19% of African Americans carry this blood type.

Question: My wife and I have are A/B-, what blood type will our child have?

Answer: Your child's rH factor will be negative, as you and your wife are both negative for this factor. The child's blood type will depend on which genes they obtain. The A and B blood types are co-dominant. Your child may obtain the A gene from both parents (25% chance of A- blood type), the B gene from both parents (25% chance of B- phenotype), or one of each (50% chance of AB-).

Question: I have a B+ blood type. My daughter is O+ and my son is B+. My husband forgot his blood type. Can you figure what blood type my husband is?