Allelic Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Allelic and links to relevant pages within the course.
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| A, B, and O Genes The ABO locus is on chromosome number 9. There are three major allelic genes and numerous rare genes. The three principle genes are A, B, and O. The A gene determines the product N-acetylgalactosaminyltranferase activity. The B gene determines galactosyltransferase activity. The O gene does not produce a functional enzyme. The enzyme products of the A and/or B genes act on H substance to convert it to A and/or B antigens. Not all H substance is converted; thus, all cells normally contain some H substance along with the A and/or B antigens. If both the A and B genes are present, some H antigen sites are converted to A antigen and other H antigen sites are converted to B antigen. (A single antigen site does not have both A and B antigens.) The O gene is an amorph and doesn’t act on H substance, therefore group O cells contain only H substance. See the diagram on the next page. | View Page |
| Inherited Genes The A, B, and H antigens, like many other blood group antigens, are the expression of genes inherited from the previous generation. If the antigen is demonstrated, the gene controlling it must have been inherited from one or both of the parents. As previously mentioned, the genes A, B, and O are allelic genes. Assuming the production of H substance, these three genes, in various possible combinations of two, account for the four recognized ABO groups: A, B, AB, and O. Each individual inherits two ABO genes, one from each parent, and these genes determine which ABO antigen will be present on that individual’s red cells. These genes exhibit co-dominance, meaning that if both A and B genes are present, both will be expressed. | View Page |