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CATEGORIES:Cambridge Evolutionary Genetics
SUMMARY:Journal Club: Molecular Evolution of a Y Chromosom
 e to Autosome Gene Duplication in Drosophila - Joh
 n Welsh
DTSTART;TZID=Europe/London:20110317T130000
DTEND;TZID=Europe/London:20110317T140000
UID:TALK29576AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/29576
DESCRIPTION:Dyer et al. Mol Biol Evol (2011) 28(3):1293-1306. 
   \n\nIn contrast to the rest of the genome\, the 
 Y chromosome is restricted to males and lacks reco
 mbination. As a result\, Y chromosomes are unable 
 to respond efficiently to selection\, and newly fo
 rmed Y chromosomes degenerate until few genes rema
 in. The rapid loss of genes from newly formed Y ch
 romosomes has been well studied\, but gene loss fr
 om highly degenerate Y chromosomes has only recent
 ly received attention. Here\, we identify and char
 acterize a Y to autosome duplication of the male f
 ertility gene kl-5 that occurred during the evolut
 ion of the testacea group species of Drosophila. T
 he duplication was likely DNA based\, as other Y-l
 inked genes remain on the Y chromosome\, the locat
 ions of introns are conserved\, and expression ana
 lyses suggest that regulatory elements remain link
 ed. Genetic mapping reveals that the autosomal cop
 y of kl-5 resides on the dot chromosome\, a tiny a
 utosome with strongly suppressed recombination. Mo
 lecular evolutionary analyses show that autosomal 
 copies of kl-5 have reduced polymorphism and littl
 e recombination. Importantly\, the rate of protein
  evolution of kl-5 has increased significantly in 
 lineages where it is on the dot versus Y linked. F
 urther analyses suggest this pattern is a conseque
 nce of relaxed purifying selection\, rather than a
 daptive evolution. Thus\, although the initial fix
 ation of the kl-5 duplication may have been advant
 ageous\, slightly deleterious mutations have accum
 ulated in the dot-linked copies of kl-5 faster tha
 n in the Y-linked copies. Because the dot chromoso
 me contains seven times more genes than the Y and 
 is exposed to selection in both males and females\
 , these results suggest that the dot suffers the d
 eleterious effects of genetic linkage to more sele
 ctive targets compared with the Y chromosome. Thus
 \, a highly degenerate Y chromosome may not be the
  worst environment in the genome\, as is generally
  thought\, but may in fact be protected from the a
 ccumulation of deleterious mutations relative to o
 ther nonrecombining regions that contain more gene
 s.
LOCATION:First Floor Seminar Room\, Department of Zoology
CONTACT:Simon Baxter
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