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1
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68549133539
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The evolutionary enigma of sex
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This review, by one of the leading theorists in evolutionary genetics, summarizes theoretical work on the evolution of sex in a clear, accessible way, sidestepping the sometimes formidable math, and interprets some of the attempts to test it experimentally. An excellent introduction to current thinking on the subject.
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Otto S.P. The evolutionary enigma of sex. Am Nat 174 (2009) S1-S14. This review, by one of the leading theorists in evolutionary genetics, summarizes theoretical work on the evolution of sex in a clear, accessible way, sidestepping the sometimes formidable math, and interprets some of the attempts to test it experimentally. An excellent introduction to current thinking on the subject.
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Am Nat
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Otto, S.P.1
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2
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40149100691
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The evolution of the mating-type locus: the Basidiomycetes
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Heitman J., Kronstad J.W., Taylor J.W., and Casselton L.A. (Eds), ASM Press
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Fraser J.A., Hsueh Y.-P., Findley K.M., and Heitman J. The evolution of the mating-type locus: the Basidiomycetes. In: Heitman J., Kronstad J.W., Taylor J.W., and Casselton L.A. (Eds). Sex in Fungi: Molecular Determination and Evolutionary Implications (2007), ASM Press 19-34
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Sex in Fungi: Molecular Determination and Evolutionary Implications
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Fraser, J.A.1
Hsueh, Y.-P.2
Findley, K.M.3
Heitman, J.4
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3
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68949128584
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Homothallic and heterothallic mating in the opportunistic pathogen Candida albicans
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Following up on recent observations of heterothallic mating between diploid C. albicans that are homozygous for mating type (a/a or α/α; see [20]) these authors add the surprising discovery that homothallic mating among a/a cells can be induced by the presence of α pheromone, which can come either from nearby α/α cells or from the a/a cells themselves if their BAR1 gene, which encodes a protease that normally deactivates the α pheromone that a/a cells produce, is deleted. There have been numerous switches between heterothallism and homothallism in the evolutionary history of fungi, and the Δbar1 mutation used here provides one hypothetical example of how easily that evolutionary switch could happen.
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Alby K., Schaefer D., and Bennett R.J. Homothallic and heterothallic mating in the opportunistic pathogen Candida albicans. Nature 460 (2009) 890-894. Following up on recent observations of heterothallic mating between diploid C. albicans that are homozygous for mating type (a/a or α/α; see [20]) these authors add the surprising discovery that homothallic mating among a/a cells can be induced by the presence of α pheromone, which can come either from nearby α/α cells or from the a/a cells themselves if their BAR1 gene, which encodes a protease that normally deactivates the α pheromone that a/a cells produce, is deleted. There have been numerous switches between heterothallism and homothallism in the evolutionary history of fungi, and the Δbar1 mutation used here provides one hypothetical example of how easily that evolutionary switch could happen.
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(2009)
Nature
, vol.460
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Alby, K.1
Schaefer, D.2
Bennett, R.J.3
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4
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58749112527
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Discovery of a sexual cycle in the opportunistic fungal pathogen Aspergillus fumigatus
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The sexuality of this significant pathogen had been suspected for about a decade based on genomic evidence of recombination and genes involved in mating. What is remarkable about this study is that where others had failed for over a century, the authors finally hit upon the right environmental triggers to observe directly the heterothallic sexual cycle of A. fumigatus, after setting up crosses and giving them half a year to sporulate.
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O'Gorman C.M., Fuller H.T., and Dyer P.S. Discovery of a sexual cycle in the opportunistic fungal pathogen Aspergillus fumigatus. Nature 457 (2009) 471-475. The sexuality of this significant pathogen had been suspected for about a decade based on genomic evidence of recombination and genes involved in mating. What is remarkable about this study is that where others had failed for over a century, the authors finally hit upon the right environmental triggers to observe directly the heterothallic sexual cycle of A. fumigatus, after setting up crosses and giving them half a year to sporulate.
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(2009)
Nature
, vol.457
, pp. 471-475
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O'Gorman, C.M.1
Fuller, H.T.2
Dyer, P.S.3
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5
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66649105285
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Evolution of pathogenicity and sexual reproduction in eight Candida genomes
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This massive study presents some unnerving surprises, in particular that while apparently asexual Candida species have conserved pheromone response pathways, known sexual ones lack genes that are fundamental to mating-type determination and meiosis in S. cerevisiae - unnerving because they call into question the reliability of the 'model system' approach to learning about pathogenic yeasts.
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Butler G., Rasmussen M.D., Lin M.F., Santos M.A.S., Sakthikumar S., Munro C.A., Rheinbay E., Grabherr M., Forche A., Reedy J.L., et al. Evolution of pathogenicity and sexual reproduction in eight Candida genomes. Nature 459 (2009) 657-662. This massive study presents some unnerving surprises, in particular that while apparently asexual Candida species have conserved pheromone response pathways, known sexual ones lack genes that are fundamental to mating-type determination and meiosis in S. cerevisiae - unnerving because they call into question the reliability of the 'model system' approach to learning about pathogenic yeasts.
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(2009)
Nature
, vol.459
, pp. 657-662
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Butler, G.1
Rasmussen, M.D.2
Lin, M.F.3
Santos, M.A.S.4
Sakthikumar, S.5
Munro, C.A.6
Rheinbay, E.7
Grabherr, M.8
Forche, A.9
Reedy, J.L.10
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6
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62649089109
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Population genomics of domestic and wild yeasts
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The largest scale survey of Saccharomyces genomics so far, this analysis of 72 S. cerevisiae and 70 S. paradoxus genomes confirmed high levels of inbreeding and identified genetically distinct lineages in both species, and supported earlier studies showing more divergence between and no recombination among the S. paradoxus lineages. In S. cerevisiae, by contrast, recombination between lineages has generated 'mosaic' genomes of diverse ecotypes, including lab and fermenting strains, wild isolates, and emerging opportunistic pathogens.
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Liti G.C.D., Moses A.M., Warringer J., Parts L., James S.A., Davey R.P., Roberts I.N., Burt A., Koufopanou V., Tsai I.J., et al. Population genomics of domestic and wild yeasts. Nature 458 (2009) 337-341. The largest scale survey of Saccharomyces genomics so far, this analysis of 72 S. cerevisiae and 70 S. paradoxus genomes confirmed high levels of inbreeding and identified genetically distinct lineages in both species, and supported earlier studies showing more divergence between and no recombination among the S. paradoxus lineages. In S. cerevisiae, by contrast, recombination between lineages has generated 'mosaic' genomes of diverse ecotypes, including lab and fermenting strains, wild isolates, and emerging opportunistic pathogens.
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(2009)
Nature
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Liti, G.C.D.1
Moses, A.M.2
Warringer, J.3
Parts, L.4
James, S.A.5
Davey, R.P.6
Roberts, I.N.7
Burt, A.8
Koufopanou, V.9
Tsai, I.J.10
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7
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33846589871
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Increased outbreeding in yeast in response to dispersal by an insect vector
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This entertaining step toward bringing some natural yeast ecology into the lab shows that being eaten by Drosophila could be a mechanism of both dispersal and outcrossing for spores, which are released by the digestion of ascus walls and excreted as separated spores.
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Reuter M., Bell G., and Greig D. Increased outbreeding in yeast in response to dispersal by an insect vector. Curr Biol 15 (2007) R81-R83. This entertaining step toward bringing some natural yeast ecology into the lab shows that being eaten by Drosophila could be a mechanism of both dispersal and outcrossing for spores, which are released by the digestion of ascus walls and excreted as separated spores.
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(2007)
Curr Biol
, vol.15
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Reuter, M.1
Bell, G.2
Greig, D.3
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8
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62649126517
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Comprehensive polymorphism survey elucidates population structure of Saccharomyces cerevisiae
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Published alongside [6], this study focused on S. cerevisiae alone, and more on comparative genomics and less on its history of recombination. It corroborated the repeated origin of opportunistically pathogenic strains, and found that linkage disequilibrium is less extensive in wine strains than in other types.
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Schacherer J., Shapiro J.A., Ruderfer D.M., and Kruglyak K. Comprehensive polymorphism survey elucidates population structure of Saccharomyces cerevisiae. Nature 458 (2009) 342-346. Published alongside [6], this study focused on S. cerevisiae alone, and more on comparative genomics and less on its history of recombination. It corroborated the repeated origin of opportunistically pathogenic strains, and found that linkage disequilibrium is less extensive in wine strains than in other types.
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(2009)
Nature
, vol.458
, pp. 342-346
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Schacherer, J.1
Shapiro, J.A.2
Ruderfer, D.M.3
Kruglyak, K.4
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9
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33748288159
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Population genomic analysis of outcrossing and recombination in yeast
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The goal of this innovative study was similar to that of Tsai et al. [22]: to estimate the number of recombination events since three unrelated S. cerevisiae strains diverged from their last common ancestor. The breakpoints of recombination events were identified as sites where the phylogenetic histories at a SNP changed. What were counted was not random matings, but random matings that were detectable because of genetic differences between mates. The figure arrived at was double the frequency of outcrossing that Tsai et al. inferred for S. paradoxus, very similar given the different analyses of different species.
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Ruderfer D.M., Pratt S.C., Seidel H.S., and Kruglyak L. Population genomic analysis of outcrossing and recombination in yeast. Nat Genet 38 (2006) 1077-1081. The goal of this innovative study was similar to that of Tsai et al. [22]: to estimate the number of recombination events since three unrelated S. cerevisiae strains diverged from their last common ancestor. The breakpoints of recombination events were identified as sites where the phylogenetic histories at a SNP changed. What were counted was not random matings, but random matings that were detectable because of genetic differences between mates. The figure arrived at was double the frequency of outcrossing that Tsai et al. inferred for S. paradoxus, very similar given the different analyses of different species.
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(2006)
Nat Genet
, vol.38
, pp. 1077-1081
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Ruderfer, D.M.1
Pratt, S.C.2
Seidel, H.S.3
Kruglyak, L.4
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10
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33847259191
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Allopatric divergence, secondary contact, and genetic isolation in wild yeast populations
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Among the first studies of the genetic structure of natural S. paradoxus populations, this paper refutes, at least for yeast, the 'everything is everywhere' view of microbial biogeography. It also hints at ongoing allopatric speciation where two strongly divergent clades are sympatric in Pennsylvania. It would be intriguing if this classic mechanism of plant and animal speciation turned out to apply equally well to an organism in which outcrossing, and therefore the opportunity for selection against mismating, seem so rare.
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Kuehne H.A., Murphy H.A., Francis C.A., and Sniegowski P.D. Allopatric divergence, secondary contact, and genetic isolation in wild yeast populations. Curr Biol 17 (2007) 407-411. Among the first studies of the genetic structure of natural S. paradoxus populations, this paper refutes, at least for yeast, the 'everything is everywhere' view of microbial biogeography. It also hints at ongoing allopatric speciation where two strongly divergent clades are sympatric in Pennsylvania. It would be intriguing if this classic mechanism of plant and animal speciation turned out to apply equally well to an organism in which outcrossing, and therefore the opportunity for selection against mismating, seem so rare.
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Curr Biol
, vol.17
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Kuehne, H.A.1
Murphy, H.A.2
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Sniegowski, P.D.4
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Population genetics of the wild yeast Saccharomyces paradoxus
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Johnson L.J., Koufopanou V., Goddard M.R., Hetherington S.M.S., and Burt A. Population genetics of the wild yeast Saccharomyces paradoxus. Genetics 166 (2004) 43-52
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Genetics
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Johnson, L.J.1
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Hetherington, S.M.S.4
Burt, A.5
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12
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Sex increases the efficacy of natural selection in experimental yeast populations
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Goddard M.R., Godfrey H.C.J., and Burt A. Sex increases the efficacy of natural selection in experimental yeast populations. Nature 434 (2005) 636-640
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Nature
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Goddard, M.R.1
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Isolates of Cryptococcus neoformans from infected animals reveal genetic exchange in unisexual, α mating type populations
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Bui T., Lin X., Malik R., Heitman J., and Carter D. Isolates of Cryptococcus neoformans from infected animals reveal genetic exchange in unisexual, α mating type populations. Eukaryot Cell 7 (2008) 1771-1780
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Eukaryot Cell
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Bui, T.1
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Carter, D.5
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67249157866
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Rapid global expansion of the fungal disease Chytridiomycosis into declining and healthy amphibian populations
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This study of a pathogen that has recently become a threat to numerous amphibians indicates that the global pandemic is largely the clonal expansion of a single lineage, implying that genetic variation has been surprisingly irrelevant to the adaptation of a virulent pathogen to very divergent groups of amphibians.
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James T.Y., Litvintseva A.P., Vilgalys R., Morgan J.A.T., Taylor J.W., Fisher M.C., Berger L., Weldon C., du Preez L., Joyce E., and Longcore JE. Rapid global expansion of the fungal disease Chytridiomycosis into declining and healthy amphibian populations. PLoS Pathog 5 (2009) 1-12. This study of a pathogen that has recently become a threat to numerous amphibians indicates that the global pandemic is largely the clonal expansion of a single lineage, implying that genetic variation has been surprisingly irrelevant to the adaptation of a virulent pathogen to very divergent groups of amphibians.
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PLoS Pathog
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James, T.Y.1
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Morgan, J.A.T.4
Taylor, J.W.5
Fisher, M.C.6
Berger, L.7
Weldon, C.8
du Preez, L.9
Joyce, E.10
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The effects of sex and mutation rate on adaptation in test tubes and to mouse hosts in Saccharomyces cerevisiae
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Grimberg B., and Zeyl C. The effects of sex and mutation rate on adaptation in test tubes and to mouse hosts in Saccharomyces cerevisiae. Evolution 59 (2005) 431-438
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MAT, mating, switching and pathogenesis in Candida albicans, Candida dubliniensis, and Candida glabrata
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Soll, D.R.1
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Otto S.P. The advantages of segregation and the evolution of sex. Genetics 164 (2003) 1099-1118
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Magee P.T., and Magee B.B. Through a glass opaquely: the biological significance of mating in Candida albicans. Curr Opin Microbiol 7 (2004) 661-665
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Nielsen K., Cox G.M., Wang P., Toffaletti D.L., Perfect J.R., and Heitman J. Sexual cycle of Cryptococcus neoformans var. grubii and virulence of congenic a and α isolates. Infect Immun 71 (2003) 4831-4841
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Population genomics of the wild yeast Saccharomyces paradoxus: quantifying the life cycle
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This is an ambitious attempt to estimate the frequencies of asexual budding, within-tetrad mating, homothallic selfing, and outcrossing by comparing sequence diversity and genotype diversity (linkage disequilibrium) among 20 strains at chromosomes III, where the decline in heterozygosity with increasing distance from the obligately heterozygous MAT locus provides a measure of the relative frequencies of within-tetrad mating and selfing. The calculations make use of an old, indirect, and weakly supported estimate of per-nucleotide mutation rates, but certainly confirm the expectation from lab studies that, like S. cerevisiae, S. paradoxus is a highly inbred species.
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Tsai I.J., Bensasson D., Burt A., and Koufopanou V. Population genomics of the wild yeast Saccharomyces paradoxus: quantifying the life cycle. Proc Natl Acad Sci U S A 105 (2008) 4957-4962. This is an ambitious attempt to estimate the frequencies of asexual budding, within-tetrad mating, homothallic selfing, and outcrossing by comparing sequence diversity and genotype diversity (linkage disequilibrium) among 20 strains at chromosomes III, where the decline in heterozygosity with increasing distance from the obligately heterozygous MAT locus provides a measure of the relative frequencies of within-tetrad mating and selfing. The calculations make use of an old, indirect, and weakly supported estimate of per-nucleotide mutation rates, but certainly confirm the expectation from lab studies that, like S. cerevisiae, S. paradoxus is a highly inbred species.
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Proc Natl Acad Sci U S A
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Tsai, I.J.1
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48949109664
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The origin of multiple mating types in the model mushrooms Coprinopsis cinerea and Schizophyllum commune
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Heitman J.K.J., Taylor J.W., and Casselton L.A. (Eds), ASM Press
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Epistatic buffering of fitness loss in yeast double deletion strains
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An arduous study comparing the effects on growth rates of 758 single ORF deletions and 639 pairs of them, testing for the predominantly negative epistatic interactions required by the hypothesis that a major benefit of recombination is the concentration of harmful mutations into fewer offspring, allowing more efficient selection against mutations. On average epistasis was weakly positive, although not pointed out was a tendency for the weakly harmful mutations, which would be more persistent in a population and contribute more to linkage disequilibrium than more strongly harmful ones, to be negatively epistatic to each other.
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Jasnos L., and Korona R. Epistatic buffering of fitness loss in yeast double deletion strains. Nat Genet 39 (2007) 550-554. An arduous study comparing the effects on growth rates of 758 single ORF deletions and 639 pairs of them, testing for the predominantly negative epistatic interactions required by the hypothesis that a major benefit of recombination is the concentration of harmful mutations into fewer offspring, allowing more efficient selection against mutations. On average epistasis was weakly positive, although not pointed out was a tendency for the weakly harmful mutations, which would be more persistent in a population and contribute more to linkage disequilibrium than more strongly harmful ones, to be negatively epistatic to each other.
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