• Question: * Star Question * What causes different types of blood in people and why is AB negative blood so rare? - Thiyanagi, Live Chat

    Asked by on 30 Jun 2020. This question was also asked by .
    • Photo: Donna MacCallum

      Donna MacCallum answered on 30 Jun 2020: last edited 30 Jun 2020 12:23 pm

      This is a great question and one that involved genetics…

      Your blood group is determined by blood group antigen genes and we all have two copies… blood group A = AA or AO; group B = BB or BO; group AB = AB and group O= OO (where O is recessive and is masked by either A or B; A and B are co-dominant).

      This is complicated by the frequency of each gene type… O occurs more frequently in the western population than A or B, so even though it is recessive blood group O is very frequent.

      In the USA, 44% have blood group O, 42% have blood group A, 10% have blood group B and 4% have blood group AB. Similar in the UK: 47% have blood group O, 39% have blood group A, 10% have blood group B and 4% have blood group AB.
      However, blood group B is much higher in India, Bangladesh, Pakistan, Korea and some other countries (https://en.wikipedia.org/wiki/Blood_type_distribution_by_country – note that this data is not completely accurate). In these countries, AB is higher too.

      Blood groups are then further divided by whether you are Positive or Negative… with positive blood groups making up 80-90% of the population and Negative blood groups rarer… so AB negative is the rarest blood group

      hope that helps!

    • Photo: Candice Ashmore-Harris

      Candice Ashmore-Harris answered on 30 Jun 2020:

      As Donna has said, your blood type is determined by the type of antigens stuck on the surface of your red blood cells. These antigens can either be made up of proteins or complexes of sugar molecules (polysaccharides) and which antigens you have depends on your genetic code (DNA). You can only make the antigens that you have the code for and you inherit this code from your parents. What ABO blood group you have is determined by which two antigen codes you get from your parents. To be AB you need to inherit one code for A and one from B from each your parents. To be blood type A or blood type B you can either inherit two AAs or two BBs or OA or OB because O represents no antigen presence. This is also why those with blood group O (where they have OO as their blood type) are considered universal donors, because there are no antigens on the surface to cause an immune reaction if received by someone with A or B antigens. Whether blood is positive of negative (e.g. AB-, B+) is determined by whether you have the rhesus D antigen (Rh), it’s another type of blood group system and it is important Rh+ blood isn’t given to a Rh- patient because this would cause an immune reaction.

      Despite knowing about different blood types existing since the 1900s we still don’t really know if there’s a particular benefit or reason for having different kinds. It may be that certain blood groups are more susceptible to particular infections and so certain blood types have been naturally selected for in different areas, but more study is needed for anyone to be very confident about this. AB blood types are rarer than A, B or O because you have a statistically lower chance of receiving the code for both antigens from your parents compared to the frequency of O and the AB antigens present in the population.

      If you’d like to read a bit further the NHS website can tell you how common different blood types are in the UK: https://www.nhs.uk/conditions/blood-groups/ and you can also read a bit more about the history of the different blood types here: https://www.smithsonianmag.com/science-nature/the-mystery-of-human-blood-types-86993838/ and here: https://www.bbc.com/future/article/20140715-why-do-we-have-blood-types

    • Photo: Roy Drissen

      Roy Drissen answered on 30 Jun 2020:

      Blood groups are determined by your genes, and thus it is inherited. There is one gene that determines if your bloodgroup is negative or positive. This is the Rhesus gene. If you have the gene, your bloodgroup is positive, if you don’t have it your bloodgroup is negative. Most people have this gene, and therefor a bloodgroup negative is not as common as positive.
      The ABO bloodgroups is also determined by your inherited genes, but is a little more tricky. There are 3 genes: gene a, gene b and gene o. But everyone only has 2 genes (one inherited from mother, and one from father). That means that there are 6 possible gene combination you can have: aa, ab, ao, bb, bo and oo. (The order does not matter, so ab is the same as ba). The combination of these genes determine your bloodgroup according to these rules: aa and ao become bloodgroup A, bb and bo become bloodgroup B, ab becomes bloodgroup AB, and oo becomes bloodgroup O. Now gene a and gene o are a lot more common than gene b. As a result, the chance of getting bloodgroup AB is less likely, than bloodgroup A or O.
      In short, the bloodgroups are inherited, just like the color or your hair and eyes. And bloodgroup AB negative is not very common, similarly how blond hair is less common than brown hair, or green eyes are less common than brown eyes.

    • Photo: Gulnar Abdullayeva

      Gulnar Abdullayeva answered on 30 Jun 2020: last edited 30 Jun 2020 2:21 pm

      Hi. Interesting question! There are already great answers.

      Generally, 4 main well-known blood types are well-known – A, B, AB, and O, which are first discovered by Karl Landsteiner in 1900. Each blood type refers to a specific marker on a red blood cell. These types are formed by antibodies and antigens in our blood. Antibodies are proteins produced by the immune system that can recognise, analyse, and if needed destroy or neutralize an antigen, which triggers immune response. Antigens are mostly viral or bacterial invaders that can cause infections or diseases. Our immune system will usually recognise, label and get rid of them. But there are also antigens are produced by our bodies, called self-antigens, which our immune system will not affect them.

      The whole ABO blood system is built upon on the sugar-based self-antigens and corresponding antibodies. Type A means you have A antigens on the red blood cells and anti-B antibodies in the plasma. People with type B have B antigens on the red blood cell with anti-A antibodies floating around. AB blood type has both A and B antigens, but no antibodies in their plasma whereas type O blood has no antigens, but have A and B antibodies. In addition, a positive or negative symbol that comes after your ABO blood type is based on Rhesus Blood Group System. It is related to the presence or absence of rhesus D antigen (Rh). A body with Rh negative blood will reject Rh positive blood.

      But which blood type we have is determined by ABO genes, which has different alleles: A, B, and O. We have 2 alleles of A, B, or O genes; one allele comes from a mother, one from a father.
      People with AB blood is a result of getting an A gene from one parent and a B gene from the other. Based on the number of people in the A and B blood types, the frequency of that particular combination is simply lower than any other possibility. This is one reason why AB is a rare type.

      You can find more information: https://www.medicaldaily.com/ab-blood-type-red-blood-cells-379342

      I hope that answers your question! Thank you.

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