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SUMMARY:Journal Club: Molecular Evolution of a Y Chromosome to Autosome Ge
 ne Duplication in Drosophila - John Welsh
DTSTART:20110317T130000Z
DTEND:20110317T140000Z
UID:TALK29576@talks.cam.ac.uk
CONTACT:Simon Baxter
DESCRIPTION:Dyer et al. Mol Biol Evol (2011) 28(3):1293-1306.   \n\nIn con
 trast to the rest of the genome\, the Y chromosome is restricted to males 
 and lacks recombination. As a result\, Y chromosomes are unable to respond
  efficiently to selection\, and newly formed Y chromosomes degenerate unti
 l few genes remain. The rapid loss of genes from newly formed Y chromosome
 s has been well studied\, but gene loss from highly degenerate Y chromosom
 es has only recently received attention. Here\, we identify and characteri
 ze a Y to autosome duplication of the male fertility gene kl-5 that occurr
 ed during the evolution of the testacea group species of Drosophila. The d
 uplication was likely DNA based\, as other Y-linked genes remain on the Y 
 chromosome\, the locations of introns are conserved\, and expression analy
 ses suggest that regulatory elements remain linked. Genetic mapping reveal
 s that the autosomal copy of kl-5 resides on the dot chromosome\, a tiny a
 utosome with strongly suppressed recombination. Molecular evolutionary ana
 lyses show that autosomal copies of kl-5 have reduced polymorphism and lit
 tle recombination. Importantly\, the rate of protein evolution of kl-5 has
  increased significantly in lineages where it is on the dot versus Y linke
 d. Further analyses suggest this pattern is a consequence of relaxed purif
 ying selection\, rather than adaptive evolution. Thus\, although the initi
 al fixation of the kl-5 duplication may have been advantageous\, slightly 
 deleterious mutations have accumulated in the dot-linked copies of kl-5 fa
 ster than in the Y-linked copies. Because the dot chromosome contains seve
 n times more genes than the Y and is exposed to selection in both males an
 d females\, these results suggest that the dot suffers the deleterious eff
 ects of genetic linkage to more selective targets compared with the Y chro
 mosome. Thus\, a highly degenerate Y chromosome may not be the worst envir
 onment in the genome\, as is generally thought\, but may in fact be protec
 ted from the accumulation of deleterious mutations relative to other nonre
 combining regions that contain more genes.
LOCATION:First Floor Seminar Room\, Department of Zoology
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