Oooc oc

Molecular structure of blood type. A, B, and O antigens differ in the presence and type of the terminal sugar on a common glycoprotein base. The genes for A, B, and O blood type code for enzymes that add these sugars. Adapted from <http://www.indstate .edu/thcme/mwking/ abo-bloodgroups.gif>.

least one Se gene is a secretor. Approximately 77 percent of Europeans are secretors. This frequency is rarely less than 50 percent and sometimes as high as 100 percent in other populations.

An interesting aspect of the ABO blood groups is their association with disease. Among individuals with stomach and peptic ulcers, there is an excess of type O individuals, whereas among those with cancer of the stomach, there is an excess of type A individuals. Not all type O individuals have an increased risk for peptic or stomach ulcers, however. If type O individuals are secretors, they are protected against ulceration, whereas non-secretors have a two-fold increased risk. Thus the presence of ABO blood group substances act as a protective agent against the development of stomach and peptic ulcers.

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