Locus Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Locus and links to relevant pages within the course.
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| The H gene Three separate loci (ABO, Hh, and Se) contain the genes that control the location and occurrence of the A and B antigens. Hh and Se genes are closely linked on chromosome 19. The precursor substance is acted upon by the H gene and is converted to H substance. The product of the H gene is an enzyme fucosyltransferase, responsible for attaching fucose to the terminal galactose of the precursor substance on the RBC membrane and thus forming H substance. There are only two recognized alleles at this locus: the active form, H, and an amorph, h. The H gene is a high-incidence gene. People who inherit hh are extremely rare. Since the h gene is amorphic, it does not act on the precursor substance. | View Page |
| 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 |