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Name: Taylor
Status: Student
Grade:  9-12
Location: NY
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.

Van Hoeck

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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