Molecular Biology and Evolution, Vol 10, 48-59, Copyright © 1993 by Society for Molecular Biology and Evolution
J Klein, C O'hUigin, F Figueroa, WE Mayer and D Klein
The human major histocompatibility complex (Mhc) is a chromosomal segment
approximately 4 million bp long that contains > or = 84 genes. Some of
these genes code for the class I and class II molecules, while the
remaining genes code for complement components, cytochrome P450, tumor
necrosis factor, and many other, unrelated proteins. We demonstrate on
three examples (DP, C4-CYP21, and DRB) that different regions of the Mhc
have different evolutionary histories. The organization of the DP region,
which in humans contains four genes, was established in the ancestral
Anthropoidea or earlier and has not changed since. The duplication that
generated the two C4-CYP21 modules occurred in the ancestral Catarrhini or
earlier, but the region has been undergoing periodic homogenizations via
unequal crossing-over, which make paralogous genes in the same species more
similar to each other than to orthologous genes of different species. The
eight or nine genes of the DRB region were also generated in the ancestral
Catarrhini, but the region has since been subject to frequent
rearrangements, which generated various DRB haplotypes. Not only the
alleles but, in part, also the haplotype polymorphism is evolving
transspecifically. The DRB region of the Platyrrhini has an origin
different from that of the Catarrhini. The picture emerging from these
studies is that of both stability in some regions of the Mhc and tremendous
evolutionary instability in other regions.
ORIGINAL ARTICLE
Different modes of Mhc evolution in primates
Max-Planck-Institut fur Biologie, Abteilung Immungenetik, Tubingen, Federal Republic of Germany.
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