The gene conversion hypothesis of MHC evolution: a review

Martinsohn, Jann T.; Sousa, Ana Berta; Guethlein, Libby; Howard, Jonathan

doi:10.1007/s002510050593

Cited by 122 publications

(99 citation statements)

References 242 publications

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“…Pfau et al (2001) found concordance between species and gene trees for an MHC DQA locus when comparing alleles from the cotton rat (Sigmondon hisipidus) with other rodents. Moreover, mutational processes such as gene conversion and interlocus recombination can bias analysis by affecting divergence and retention times (Martinsohn et al, 1999). As such, some MHC alleles may be considerably younger than they would appear from an MHC-based phylogeny.…”

Section: Detecting Selection In Contemporary Populationsmentioning

confidence: 99%

The evolutionary ecology of the major histocompatibility complex

2005

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The major histocompatibility complex (MHC) has become a paradigm for how selection can act to maintain adaptively important genetic diversity in natural populations. Here, we review the contribution of studies on the MHC in non-model species to our understanding of how selection affects MHC diversity, emphasising how ecological and ethological processes influence the tempo and mode of evolution at the MHC, and conversely, how variability at the MHC affects individual fitness, population dynamics and viability. We focus on three main areas: the types of information that have been used to detect the action of selection on MHC genes; the relative contributions of parasite-mediated and sexual selection on the maintenance of MHC diversity; and possible future lines of research that may help resolve some of the unanswered issues associated with MHC evolution.

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Section: Detecting Selection In Contemporary Populationsmentioning

confidence: 99%

The evolutionary ecology of the major histocompatibility complex

2005

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“…Numerous studies suggest that these high levels of variability are maintained by natural and sexual selection in a wide range of organisms (reviewed by Apanius et al 1997;Jordan and Bruford 1998;Bernatchez and Landry 2003). MHC variation is generated and new alleles created by point mutation and by recombination and gene conversion events between existing alleles (Belich et al 1992;Watkins et al 1992;Parham and Ohta 1996;Martinsohn et al 1999). Most of the amino acid variation is concentrated at peptide binding residues (PBRs): those amino acids responsible for binding peptides derived from pathogens.…”

Section: Introductionmentioning

confidence: 99%

Patterns of variability at the major histocompatibility class II alpha locus in Atlantic salmon contrast with those at the class I locus

et al. 2005

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In order to investigate the mechanisms creating and maintaining variability at the major histocompatibility (MH) class II alpha (DAA) locus we examined patterns of polymorphism in two isolated Atlantic salmon populations which share a common post-glacial origin. As expected from their common origin, but contrary to the observation at the MH class I locus, these populations shared the majority of DAA alleles: out of 17 sequences observed, 11 were common to both populations. Recombination seems to play a more important role in the origin of new alleles at the class II alpha locus than at the class I locus. A greater than expected proportion of sites inferred to be positively selected (potentially peptide binding residues, PBRs) were found to be involved in recombination events, suggesting a mechanism for increasing MH variability through an interaction between recombination and natural selection. Thus it appears that although selection and recombination are important mechanisms for the evolution of both class II alpha and class I loci in the Atlantic salmon, the pattern of variability differs markedly between these classes of MH loci.

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“…Multigene families whose member genes have similar functions are believed to undergo concerted evolution (for review see Martinsohn et al, 1999). During concerted evolution, gene conversion can change the number of copies of a particular allele within an individual owing to non-reciprocal exchange of DNA between two sequences at different genetic loci.…”

Section: Mhc Variation and Models Of Multigene Evolutionmentioning

confidence: 99%

Evolution of MHC class IIB in the genome of wild and ornamental guppies, Poecilia reticulata

2006

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This is the first study to quantify genomic sequence variation of the major histocompatibility complex (MHC) in wild and ornamental guppies, Poecilia reticulata. We sequenced 196-219 bp of exon 2 MHC class IIB (DAB) in 56 wild Trinidadian guppies and 14 ornamental strain guppies. Each of two natural populations possessed high allelic richness (15-16 alleles), whereas only three or fewer DAB alleles were amplified from ornamental guppies. The disparity in allelic richness between wild and ornamental fish cannot be fully explained by fixation of alleles by inbreeding, nor by the presence of non-amplified sequences (ie null alleles). Rather, we suggest that the same allele is fixed at duplicated MHC DAB loci owing to gene conversion. Alternatively, the number of loci in the ornamental strains has contracted during 4100 generations in captivity, a hypothesis consistent with the accordion model of MHC evolution. We furthermore analysed the substitution patterns by making pairwise comparisons of sequence variation at the putative peptide binding region (PBR). The rate of non-synonymous substitutions (dN) only marginally exceeded synonymous substitutions (dS) in PBR codons. Highly diverged sequences showed no evidence for diversifying selection, possibly because synonymous substitutions have accumulated since their divergence. Also, the substitution pattern of similar alleles did not show evidence for diversifying selection, plausibly because advantageous non-synonymous substitutions have not yet accumulated. Intermediately diverged sequences showed the highest relative rate of non-synonymous substitutions, with dN/dS414 in some pairwise comparisons. Consequently, a curvilinear relationship was observed between the dN/dS ratio and the level of sequence divergence.

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The gene conversion hypothesis of MHC evolution: a review

Cited by 122 publications

References 242 publications

The evolutionary ecology of the major histocompatibility complex

The evolutionary ecology of the major histocompatibility complex

Patterns of variability at the major histocompatibility class II alpha locus in Atlantic salmon contrast with those at the class I locus

Evolution of MHC class IIB in the genome of wild and ornamental guppies, Poecilia reticulata

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