| Themes > Science > Life Sciences > General Biology > Immunology > Recognition Systems in Immunity > The Major Histocompatibility Complex > Allelic Polymorphism |
The MHC is highly polymorphic. There are a large number of genetic variants (alleles) at each genetic locus. Crucially many of these alleles are represented at significant frequency (> 1%) in the population, and in addition the alleles generally differ from one another by many (up to 30) amino acid substitutions. For example in humans there are more than 200 alleles described at some MHC loci. Such a remarkable degree of polymorphism implies a selective pressure to establish and maintain it. |
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