What does blood type do?

Genes and blood types

1. Overview of blood

Blood is composed of four components: plasma, red blood cells, white blood cells, and platelets. Plasma accounts for about 55% of blood and is a mixture of water, sugar, fat, protein, potassium salts and calcium salts. Also contains many blood clot-forming chemicals necessary to stop bleeding. Blood cells and platelets make up the other 45 parts of the blood.

There are two types of blood cells: red blood cells and white blood cells. Red blood cells make up the majority and look like rings with holes in them, unable to move around. Red blood cells contain a special protein called hemoglobin, which makes red blood cells look red. It can carry oxygen from the lungs to the whole body and concentrate carbon dioxide from the whole body to the lungs. Although blood contains many non-red blood cell components, the number of red blood cells is so large that the blood itself appears red.

White blood cells are round and much larger than red blood cells. They produce proteins called antibodies that help the body fight infections caused by bacteria, viruses, and foreign substances.

Platelets are not actually cells, but just fragments of cells. When we suffer trauma, platelets gather and stick around the wound, producing chemicals that activate the coagulation mechanism, and the blood stops.

2. What is blood type

Everyone has a blood type. The most commonly used blood type classification method is the ABO classification system invented by Karl Landsteiner in the early 1920s, which includes four blood types: A, B, AB, and O. Your blood type is determined before you are born by the genes you inherit from your parents. We inherit a large number of genes, half from mother and half from father, which combine to determine blood type, producing a protein called agglutinogen that is found on the surface of red blood cells.

There are three alleles of blood type genes: A, B and O. Since everyone has two copies of the gene, there are six possible combinations: AA, BB, OO, AB, AO and BO. In genetic terms these combinations are called genotypes and contain the genes inherited from each parent.

In addition to the protein agglutinogen, which is found in red blood cells, other genes produce proteins called clotting hormones that run in the plasma. Lectins work to ensure that there are only one type of blood cells in your blood.

3. Genotype determines blood type

The agglutinogen produced by the O allele has no special enzyme activity, but the agglutinogens produced by the A and B alleles have their own of enzyme activity. Therefore, people with genotype OO have type O blood, which means that the agglutinogens on their red blood cells do not have any enzyme activity, and their blood will contain lectins A and B. Lectin A destroys type A blood cells that may enter the body's blood circulation, and lectin B destroys type B blood cells.

People with genotype AA have type A blood because the agglutinogens on their red blood cells have enzymatic activity. People with the AO genotype also have enzyme activity associated with the A allele, so they also have type A blood. (Remember that the O allele does not have any enzyme activity!) People with type A blood have lectin B in their plasma, which destroys type B blood cells that enter the body's blood circulation.

Similarly, people with genotypes BB and BO belong to type B blood. These people have lectin A in their plasma, which destroys any type B blood cells that enter the circulation.

People with genotype AB have enzyme activity related to both the A and B alleles. These people have no lectins in their plasma.

The concepts of genotype and phenotype can be easily understood from the example of blood groups. Genotype refers to the actual genes a person possesses that determine a certain characteristic, and phenotype refers to the characteristics a person exhibits. In the example of blood types, genotypes AA and AB cause people to exhibit the phenotype of blood type A. Similarly, genotypes BB and BO exhibit the phenotype of blood type B. People with phenotypes O and AB can only have one genotype, OO and AB respectively.

In different regions of the world, the distribution of people with blood types A, B, O, and AB is different. The chart below illustrates the respective proportions of each blood type in various regions of the world.

Crowd O A B AB

United States.289 .499 .132 .080

Australia.427 .391 .115 .066

India Bolivia.931 .053 .016 .001

China.439 .270 .233 .058

Denmark.423 .434 .101 .042

Eskimo. 472 .452 .059 .017

France.417 .453 .091 .039

Ireland.542 .323 .106 .029

Nigeria.515 . 214 .232 .039

White people in St. Louis, USA.453 .413 .099 .035

Black people in Iowa, USA.491 .265 .201 .043

The discovery rate of blood types is determined by the number of alleles A, B, and O found in different parts of the world. As people from around the world migrate and mix on a larger scale, the distribution of different blood types becomes more and more even.

4. What is blood transfusion?

Because there are only four blood types, it is possible to extract blood from one person and put it into another person, a process called blood transfusion. For a transfusion to be successful, the agglutinogens on the surface of the donor's red blood cells must correspond to those of the recipient. In other words, the blood types of the donor and the recipient must be compatible, otherwise the antibodies (lectins) in the recipient's blood will attack the donor's blood cells and form a blood clot through agglutination reaction.

If you need a blood transfusion, someone will take your blood sample to test your blood type to determine whose blood genotype corresponds. People with type A blood can receive blood from people with genotypes AA, AO and OO, and people with type B blood can receive blood from people with genotypes BB, BO and OO.

5. Two special blood types during blood transfusion: OO and AB

People with type O blood are called universal donors because their blood can be donated to anyone. However, They can only accept type O blood. Type O blood does not carry agglutinogens A or B. The immune system treats agglutinogens as foreign substances. People with type O blood have lectins in their plasma that fight against agglutinogens A and B. Therefore, if you have blood types A, B, or AB The body cannot avoid agglutination reactions.

People with the second special blood type, type AB, are called universal recipients because they can receive blood from all four blood types. Type AB blood has agglutinogens A and B on the surface of its red blood cells, and the body's immune system sees them as part of itself - not relics. Type AB blood cannot produce lectins against agglutogens A and B, so blood types A, B, AB, and O will not produce agglutination reactions.