title: Is the Y chromosome disappearing?--both sides of the argument.
abstract: On August 31, 2011 at the 18th International Chromosome Conference in Manchester, Jenny Graves took on Jenn Hughes to debate the demise (or otherwise) of the mammalian Y chromosome. Sex chromosome evolution is an example of convergence; there are numerous examples of XY and ZW systems with varying degrees of differentiation and isolated examples of the Y disappearing in some lineages. It is agreed that the Y was once genetically identical to its partner and that the present-day human sex chromosomes retain only traces of their shared ancestry. The euchromatic portion of the male-specific region of the Y is ~1/6 of the size of the X and has only ~1/12 the number of genes. The big question however is whether this degradation will continue or whether it has reached a point of equilibrium. Jenny Graves argued that the Y chromosome is subject to higher rates of variation and inefficient selection and that Ys (and Ws) degrade inexorably. She argued that there is evidence that the Y in other mammals has undergone lineage-specific degradation and already disappeared in some rodent lineages. She also pointed out that there is practically nothing left of the original human Y and the added part of the human Y is degrading rapidly. Jenn Hughes on the other hand argued that the Y has not disappeared yet and it has been around for hundreds of millions of years. She stated that it has shown that it can outsmart genetic decay in the absence of "normal" recombination and that most of its genes on the human Y exhibit signs of purifying selection. She noted that it has added at least eight different genes, many of which have subsequently expanded in copy number, and that it has not lost any genes since the human and chimpanzee diverged ~6 million years ago. The issue was put to the vote with an exact 50/50 split among the opinion of the audience; an interesting (though perhaps not entirely unexpected) skew however was noted in the sex ratio of those for and against the notion.
authors.affiliation: University of Kent, Canterbury, UK. d.k.griffin@kent.ac.uk
authors.forename: Darren K
authors.initials: DK
authors.lastname: Griffin
mesh_terms: D000818:Animals; D022041:Euchromatin / Q000502:physiology; D019143:Evolution, Molecular; D005260:Female; D005298:Fertility; D005796:Genes / Q000235:genetics; D056426:Genetic Loci; D006801:Humans; D008297:Male; D008322:Mammals; D008957:Models, Genetic; D010641:Phenotype; D013091:Spermatogenesis; D013737:Testis / Q000166:cytology* / Q000502:physiology; D014998:Y Chromosome / Q000235:genetics* / Q000502:physiology
chemical_list: D022041:Euchromatin
references.citation: Heredity (Edinb). 2008 Jan;100(1):92-9
references.pmid: 18000521
references.citation: Chromosome Res. 2007;15(6):721-34
references.pmid: 17605112
references.citation: Nature. 2003 Jun 19;423(6942):825-37
references.pmid: 12815422
references.citation: Chromosome Res. 2010 Sep;18(6):623-34
references.pmid: 20574822
references.citation: Cytogenet Genome Res. 2002;99(1-4):157-63
references.pmid: 12900559
references.citation: Chromosoma. 2010 Oct;119(5):519-26
references.pmid: 20443119
references.citation: Nature. 1993 Apr 22;362(6422):745-7
references.pmid: 8469284
references.citation: Cell. 2006 Mar 10;124(5):901-14
references.pmid: 16530039
references.citation: Genome Biol Evol. 2010 Jul 12;2:347-57
references.pmid: 20624739
references.citation: Integr Comp Biol. 2008 Oct;48(4):512-9
references.pmid: 21669812
references.citation: Mamm Genome. 2001 Jul;12(7):538-45
references.pmid: 11420617
references.citation: Genetics. 1987 May;116(1):161-7
references.pmid: 3596229
references.citation: Bioessays. 1995 Apr;17(4):311-20
references.pmid: 7741724
references.citation: Genetica. 2001;111(1-3):143-53
references.pmid: 11841163
references.citation: Am J Hum Genet. 2009 Dec;85(6):923-8
references.pmid: 20004767
references.citation: Philos Trans R Soc Lond B Biol Sci. 2000 Nov 29;355(1403):1563-72
references.pmid: 11127901
references.citation: Genetics. 2005 Jun;170(2):975-9
references.pmid: 15834147
references.citation: Science. 2005 Jan 7;307(5706):50-1
references.pmid: 15637257
references.citation: PLoS Genet. 2009 Feb;5(2):e1000391
references.pmid: 19229325
references.citation: Nature. 2004 Jan 22;427(6972):348-52
references.pmid: 14737167
references.citation: PLoS Biol. 2011 May;9(5):e1001062
references.pmid: 21629756
references.citation: Annu Rev Genet. 2008;42:565-86
references.pmid: 18983263
references.citation: Biol Reprod. 2000 Sep;63(3):667-76
references.pmid: 10952906
references.citation: Genetica. 2002 Jun;115(2):169-77
references.pmid: 12403171
references.citation: Nat Genet. 1996 Nov;14(3):292-9
references.pmid: 8896558
references.citation: Science. 2005 Jan 7;307(5706):108-10
references.pmid: 15528405
references.citation: Nature. 2004 May 27;429(6990):382-8
references.pmid: 15164055
references.citation: Nature. 1984 Sep 13-19;311(5982):119-23
references.pmid: 6088994
references.citation: Reprod Fertil Dev. 2001;13(7-8):665-72
references.pmid: 11999319
references.citation: Nature. 2005 Mar 17;434(7031):325-37
references.pmid: 15772651
references.citation: Nat Genet. 1999 Apr;21(4):429-33
references.pmid: 10192397
references.citation: Genetics. 2010 Sep;186(1):277-86
references.pmid: 20551442
references.citation: Chromosoma. 2007 Oct;116(5):463-70
references.pmid: 17882464
references.citation: Genome Biol. 2008;9(6):R98
references.pmid: 18554412
references.citation: Nature. 2003 Jun 19;423(6942):873-6
references.pmid: 12815433
references.citation: Genetics. 2010 Mar;184(3):769-77
references.pmid: 20026681
references.citation: Evolution. 1987 Jul;41(4):911-914
references.pmid: 28564364
references.citation: Genetics. 2008 Jul;179(3):1513-25
references.pmid: 18562655
references.citation: Nature. 2005 Sep 1;437(7055):100-3
references.pmid: 16136134
references.citation: Nature. 2010 Jan 28;463(7280):536-9
references.pmid: 20072128
references.citation: Nature. 2002 Mar 21;416(6878):323-6
references.pmid: 11907578
references.citation: Curr Biol. 2004 Aug 24;14(16):1416-24
references.pmid: 15324658
references.citation: Chromosoma. 1974 May 21;46(1):91-120
references.pmid: 4134896
references.citation: Curr Biol. 2004 Sep 21;14(18):1664-9
references.pmid: 15380069
references.citation: Nature. 2002 Feb 28;415(6875):963
references.pmid: 11875544