The INDIVIDUALIST

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Genomics

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Description

The Rh blood group system (BGS) , with more than 40 antigens, is the most complex BGS. The most significant antigen is D, followed by C, E, c, and e antigens.

Fisher-Race Theory

This theory is named after the two British workers who proposed it in the 1940's. Although too simplistic to explain this complex system, the theory is useful to explain routine inheritance of D, C, E, c, and e antigens. The main tenets of the theory are as follows:

  1. Rh inheritance is controlled by 3 closely linked loci on each chromosome of a homologous pair, According to Fisher-Race the loci are so close together that crossing over cannot occur. The three genes on one chromosome will always be inherited as a haplotype unit.
  2. Each locus has its own set of alleles which are Dd , Cc , and Ee . The D gene is dominant to the d gene, but Cc and Ee are co-dominant. Today we know that the d gene does not exist; when used it represents absence of the D gene.
  3. The 3 loci are so closely linked that crossing-over does NOT occur, and the 3 genes on one chromosome are always inherited together (Figure 1-18).

http://brie.medlabscience.med.ualberta.ca/de/genetics/images/figures/fig01-03.gif

Because crossing over cannot occur, the genotype Cde/cde is impossible in a child from this mating. Even though the father has C, d, and e genes, the Cde and cde on each chromosome are always transmitted to offspring together.

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