Blood type
Two important classifications to describe blood types in humans are ABO and Rh factor. Blood transfusions from incompatible groups can cause an immunological "transfusion reaction", resulting in hemolysis, anemia, renal failure, shock, and death.
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2 Rhesus 3 Inheritance 4 Other blood types |
Humans have the following blood types along with their respective antibodies:
ABO
Overall, the O blood type is the most common blood type in the world. The A antigen is overall more common than the B antigen. Since the AB blood type requires the presence of both A and B antigens, the AB blood type is the rarest of the ABO blood types. There are known racial and geographic distributions of the ABO blood types [1].
The precise reason why people are born with antibodies against an antigen they have never been exposed to is unknown. It is believed that some bacterial antigens are similar enough to the A and B glycoproteins, and that antibodies created against the bacteria will react to ABO-incompatible blood cells.
Austrian scientist Karl Landsteiner was awarded the Nobel Prize in Physiology or Medicine in 1930 for his work in discovering ABO blood types.
Another characteristic of blood is Rhesus factor or Rh factor. Someone either has or does not have the Rh factor on the surface of their red blood cells. This is indicated as + or -. This is often combined with the ABO type. Type O+ blood is most common, though in some areas type A prevails, and there are other areas in which as many as 80 percent of the people are type B.
Matching Rhesus factor in the ABO system is very important, as mismatching (i.e. an Rh positive donor to an Rh negative recipient) will cause hemolysis.
A second born Rh positive child of an Rh negative mother will also have hematological problems including hemolysis.
Rh factor is named after the Rhesus Monkey where the factor was first identified.
Blood groups are inherited from both parents. The ABO blood type is controlled by a single gene with three alleles: i, A, and B.
A allele gives type A, B gives type B, and i gives type O. A and B are dominant over i, so ii people have type O, AA or Ai have A, BB or Bi have type B. AB people have both phenotypes because A and B express a special dominance relationship: codominance. Thus, it is usually impossible for a type AB parent to have a type O child.
When a type AB parent has a type O child, or when one type A and one type O parent produce a type AB child, it is sometimes mistakenly assumed that the child MUST be illegitimate.
Another possible explanation is that the child or parent who tests as type O has the very rare Bombay phenotype: they have inherited two recessive alleles of the H gene, (their blood group is Oh and their genotype is "hh"), and so do not produce the "H" protein that is the precursor to the "A" and "B" antigens. It then no longer matters whether the A or B enzymes are present or not, as no A or B antigen can be produced since the precursor antigen is not present.
The rare individuals with Bombay phenotype do not express H substance on their red blood cells and therefore do not bind A or B antigens. Instead, they produce antibodies to H substance (which is present on all red cells except those of hh phenotype) as well as to both A and B antigens and are therefore compatible only with other hh donors.
Individuals with Bombay phenotype blood groups can only be transfused with blood from other Bombay phenotype individuals. Given that this condition is very rare to begin with, a person with this blood group who needs an urgent blood transfusion, may be simply out of luck, as it would be quite unlikely that any blood bank would have any in stock.
Rh is inherited the same way, except that it has two alleles and Rh is dominant. Rh Disease occurs when an Rh negative mother who has already had an Rh positive child bears another Rh positive child. The antibodies in the mother's blood react to the infant's blood. This reaction doesn't always occur and is less likely to occur if the child carries either the A or B antigen and the mother does not. In the past, Rh incompatibility could result in stillbirth or death of the mother. Rh incompatibility was until recently the most common cause of long term disability in the United States. At first, this was treated by transfusing the blood of infants who survived. At present, this affliction can be treated with certain anti-Rh(+) antisera, the most common of which is Rhogam.Rhesus
Inheritance
Bombay phenotype
Rhesus inheritance