Re: (Fwd) Re: Probability and...

Steve Clark (ssclark@facstaff.wisc.edu)
Thu, 7 Sep 1995 17:49:00 -0500

Glenn wrote:
>Steve Clark wrote:
>>>An important thing not considered here is the in humans, the MHC complex
>consists of 3 polymorphic genes each with its own set of alleles. The total
>number of alleles, 59, is actually spread among three genes, not one, which
>reduces the problem of how the polymporphism arose. <<
>
>If I have messed this up I want to be clear. The article "MHC Polymorphism
>and Human Origins", Scientific American, Dec. 1993, p. 78, has a table on
>that page of all the alleles in the MHC complex.
>As I read it, there are 3 genes, the DRB1,DRB2, and DRB3. Under the DRB1
>they list "known alleles" under each locus. I quickly counted them this
>morning and there were 60 under DRB1 (unless I miscounted) , none under DRB2,
>and 4 alleles under DRB3.

I think that this does need some clarification. The MHC gene complex is,
well, complex. For the immune system, there are class I and class II genes
(there are also class III genes which do not appear related at all to the
function of immune cells). When discussing MHC genes and their
polymorphism, especially from an evolutionary standpoint, most people talk
about the class I genes (HLA-A,B and C). The DR genes are class II genes,
of which there are more than just the DR genes.

Class I and class II genes differ by structure, function and, therefore,
relatedness. As far as I know (but I haven't kept up with the nuances of
the field) gene conversion has only been described for class I genes,
possible because there do not appear to be any class II-type pseudogenes
linked to the complex.

I had assumed that you and Graeme (sp?) were discussing class I genes, and I
took you at your word that there are "59" total alleles (I have never
counted them all, and there may others yet to be found). I will look up the
Scientific American article and see what it has to say. I'll be gone this
weekend, so I won't be able to get back to you until early next week.

Steve
____________________________________________________________________________
Steven S. Clark, Ph.D. Phone: (608) 263-9137
Associate Professor FAX: (608) 263-4226
Dept. of Human Oncology and email: ssclark@facstaff.wisc.edu
UW Comprehensive Cancer Ctr
University of Wisconsin "...a university is a collection of
Madison, WI 53792 disparate academic entrepreneurs
united only by a common grievance
over parking." Clark Kerr, former
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