MHC Polymorphism at Individual MHC Genes Appears to Have Been

question 25

Multiple Choice

MHC polymorphism at individual MHC genes appears to have been strongly selected by evolutionary pressures. In other words, there appears to be selection for maintaining hundreds to thousands of different alleles of each MHC gene in the population. This notion is based on the observation that nucleotide differences between alleles that lead to amino acid substitutions are more frequent than those that are silent substitutions (i.e., not changing the amino acid sequence of the protein) . In addition, the positions within the MHC protein where most of the allelic sequence variation occurs are not randomly distributed, but are concentrated in certain regions of the MHC protein. This latter point indicates:

• A) That some nucleotide sequences within the MHC genes are hot-spots for mutation
• B) That MHC genes are more susceptible to point mutations than to larger nucleotide deletions
• C) That MHC allelic polymorphism has been driven by selection for diversity in peptide binding specificity
• D) That MHC genes are more susceptible to all types of mutations than are other genes in the genome
• E) That MHC polymorphism has evolved to prevent pathogens that infect non-human primates from infecting humans

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