MHC question

Ian A. York iayork at
Thu Nov 25 18:22:39 EST 1999

In article <01bf3740$848f9460$481380d4 at>,
jose <bcjadg at> wrote:
>Does anybody know how many MHC genes are in a species? About 10 loci? About
>50? It´s more than 100?

You need to define your terms more clearly; admittedly, the terminology
for this is very confusing.

In humans, there are three class I and three class II MHC LOCI, as well as
a bunch of non-classical MHC loci.  (I can't remember how many
non-classical there are, but I believe that a total of 25 to 40 would be
reasonable.)  That is, if you track along a chromosome of one individual,
you'll find that many genes lined up.

If you mean, how many *alleles* are there per *locus*, then it depends
heavily on the particular locus, but the range is from one (for some
non-classical MHC) to a couple of hundred (for some loci of MHC class I,
for example).

New alleles are being defined all the time, so it's not like there's a
single definite answer.

    Ian York   (iayork at  <>
    "-but as he was a York, I am rather inclined to suppose him a
     very respectable Man." -Jane Austen, The History of England

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