Recombination and Multigene Evolution Flashcards Preview

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Flashcards in Recombination and Multigene Evolution Deck (38)
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31

When is the MHC polymorphism prone to erosion

when there is little or no parasite selection, MHC polymorphism is prone to erosion by random genetic drift, particularly in small
populations.

32

What is the issue with traditional model of balancing selection on the MHC when assuming parasites are the only agent of selection

often require unrealistically large selection coefficients
(SR0.2) to explain the observed MHC polymorphism in small populations

33

what does the fact that the MHC's islands of high linkage disequilibria (LD) interspersed by recombination hot spots suggest is happening

epistasis and genetic hitch-hiking

34

what does the traditional balancing selection models not consider

ignores the potential role of linkage and epistatic
gene–gene interactions.

35

What did the ABC model propose

recessive disease-causing mutations can accumulate in the MHC in a process similar to Muller’s ratchet
Natural selection fails to purge these mutations because
this so-called ‘sheltered load’ only rarely becomes expressed, given the large number of MHC alleles and high gene diversity

36

What reduces the effective rate of recombination in the MHC

functional epistasis and
haplotype block (haploblock) structure

37

How does Muller's ratchet affect the MHC

Because there is reduced recombination, mutations are less effectively removed

38

What reduces the selection effectiveness at removing mutation from the MHC

the reduced effective rate of recombination and the typically has a high gene diversity and large number of
alleles which makes it rare for bad alleles to be shown in the homozygous form