title: The number of mutations selected during adaptation in a laboratory population of Saccharomyces cerevisiae.
abstract: There is currently limited empirical and theoretical support for the prevailing view that adaptation typically results from the fixation of many mutations, each with small phenotypic effects. Recent theoretical work suggests that, on the contrary, most of the phenotypic change during an episode of adaptation can result from the selection of a few mutations with relatively large effects. I studied the genetics of adaptation by populations of budding yeast to a culture regime of daily hundredfold dilution and transfer in a glucose-limited minimal liquid medium. A single haploid genotype isolated after 2000 generations showed a 76% fitness increase over its ancestor. This evolved haploid was crossed with its ancestor, and tetrad dissections were used to isolate a complete series of six meiotic tetrads. The Castle-Wright estimator of the number of loci at which adaptive mutations had been selected, modified to account for linkage and variation among mutations in the size of their effect, is 4.4. The estimate for a second haploid genotype, isolated from a separate population and with a fitness gain of 60%, was 2.7 loci. Backcrosses to the ancestor with the first evolved genotype support the inference that adaptation resulted primarily from two to five mutations. These backcrosses also indicated that deleterious mutations had hitchhiked with adaptive mutations in this evolved genotype.
authors.affiliation: Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109, USA. zeylcw@wfu.edu
authors.forename: Clifford
authors.initials: C
authors.lastname: Zeyl
mesh_terms: D000064:Acclimatization; D000222:Adaptation, Physiological; D005075:Biological Evolution; D003433:Crosses, Genetic; D004843:Epistasis, Genetic; D019143:Evolution, Molecular; D005800:Genes, Fungal; D005828:Genetics, Population; D005838:Genotype; D005947:Glucose / Q000235:genetics; D006238:Haploidy; D007753:Laboratories; D008957:Models, Genetic; D009154:Mutation; D010641:Phenotype; D040641:Quantitative Trait Loci; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*; D013045:Species Specificity
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D005947:Glucose
references.citation: Genetics. 1999 Oct;153(2):949-64
references.pmid: 10511570
references.citation: Genetics. 2001 Jan;157(1):53-61
references.pmid: 11139491
references.citation: Proc Natl Acad Sci U S A. 2001 Jan 30;98(3):1113-7
references.pmid: 11158603
references.citation: Nature. 2002 Mar 21;416(6878):326-30
references.pmid: 11907579
references.citation: Evolution. 2002 Jul;56(7):1317-30
references.pmid: 12206234
references.citation: Genetics. 2002 Dec;162(4):1655-74
references.pmid: 12524340
references.citation: Science. 2003 Jan 24;299(5606):555-8
references.pmid: 12543972
references.citation: Genetics. 2003 Apr;163(4):1519-26
references.pmid: 12702694
references.citation: Genetics. 1992 Aug;131(4):987-1001
references.pmid: 1325390
references.citation: Genetics. 1965 Jan;51(1):109-19
references.pmid: 17248230
references.citation: Science. 1921 Sep 9;54(1393):223
references.pmid: 17792870
references.citation: Am Nat. 1992 Nov;140(5):725-42
references.pmid: 19426041
references.citation: Genetics. 1990 Sep;126(1):235-47
references.pmid: 2227383
references.citation: Theor Appl Genet. 1985 Mar;69(5-6):553-8
references.pmid: 24254012
references.citation: Evolution. 1998 Aug;52(4):935-949
references.pmid: 28565213
references.citation: Nature. 1983 Apr 7;302(5908):495-500
references.pmid: 6339947
references.citation: Genetics. 1981 Nov-Dec;99(3-4):541-53
references.pmid: 7343418
references.citation: Yeast. 1994 Dec;10(13):1793-808
references.pmid: 7747518
references.citation: Yeast. 1997 Dec;13(16):1563-73
references.pmid: 9509575
references.citation: Genetics. 1998 Apr;148(4):1931-9
references.pmid: 9560406
references.citation: Science. 1998 Aug 21;281(5380):1194-7
references.pmid: 9712584