title: Non-neutral processes drive the nucleotide composition of non-coding sequences in Drosophila.
abstract: The nature of the forces affecting base composition is a key question in genome evolution. There is uncertainty as to whether differences in the GC contents of non-coding sequences reflect differences in mutational bias, or in the intensity of selection or biased gene conversion. We have used a polymorphism dataset for non-coding sequences on the X chromosome of Drosophila simulans to examine this question. The proportion of GC-->AT versus AT-->GC polymorphic mutations in a locus is correlated with its GC content. This implies the action of forces that favour GC over AT base pairs, which are apparently strongest in GC-rich sequences.
authors.affiliation: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Ashworth Laboratories, King's Buildings, Edinburgh, UK. p.haddrill@ed.ac.uk
authors.forename: Penelope R
authors.initials: PR
authors.lastname: Haddrill
authors.forename: Brian
authors.initials: B
authors.lastname: Charlesworth
mesh_terms: D000818:Animals; D001482:Base Composition; D021901:DNA, Intergenic / Q000737:chemistry*; D004330:Drosophila / Q000235:genetics*; D020862:GC Rich Sequence; D049810:Genetic Speciation; D009154:Mutation; D010802:Phylogeny; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D014960:X Chromosome / Q000737:chemistry
chemical_list: D021901:DNA, Intergenic