Blood Type Proteins
Country: United States
Date: April 2005
What is it that makes one blood type different from
another blood type?
There are proteins that are found on the surface of red blood cells that
are like ID tags. (They are actually sugars attached to proteins but I am
trying to make this as simple as possible.) There are A type tags and B type
tags. Your body recognizes your "ID tags", and will also notice when cells
are around that don't belong. These different proteins make one red blood
cell type different from another. By the way, Type O blood doesn't have
these ID tags (at least not of the ABO type) and type AB has both kinds.
This phenomenon is known as genetic polymorphism. Literally, it means *many
forms* and refers to the existence of many forms of a gene or allele in high
frequencies. High means significantly higher than the frequency of typical
mutant genes like albinism or polydactyly for example. Like all genetic
variability, these genes arise by random mutation and the theory to explain
their high frequency in populations is that individuals who are heterozygous
have a selective advantage over people who are homozyous. For example, in
environments where malaria is prevalent, people who are heterozygous for the
gene for sickle-cell anemia have a selective advantage over people who are
homozygous for the sickle-cell gene or homozygous for the normal gene
because people homozygous for sickle-cell die of sicle-cell disease and
people homozygous for the normal gene are more susceptible to malaris
whereas people that are heterozygous are partially resistant to malaria.
Ron Baker, Ph.D.
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Update: June 2012