title: On the location of the gene(s) harbouring the advantageous variant that maintains the X/4 fusion of Drosophila americana.
abstract: Weak selection is maintaining the Drosophila americana X/4 fusion chromosomal frequency cline. The gene(s) harbouring the advantageous variant(s) that is responsible for the establishment and maintenance of this chromosomal frequency gradient must be located in a region of the X and/or 4th chromosome that is genetically isolated between the X/4 fusion and non-fusion forms. The limits of these regions must thus be determined before an attempt is made to identify these genes. For this purpose, the correspondence between the D. virilis X and 4th chromosome genome scaffolds sequence and the D. americana gene order was established. Polymorphism levels and patterns at seven genes located at the base of the D. americana X chromosome, as well as three genes located at the base of the 4th chromosome, were analysed. The data suggest that the D. americana X/4 fusion is no more than 29,000 years old. At the base of the X chromosome, there is suppression of recombination within X/4 fusion and non-fusion chromosomes, and little recombination between the two chromosomal forms. Apparent fixed silent and replacement differences are found in three of seven genes analysed located at the base of the X chromosome. There is no evidence for suppression of recombination between fusion and non-fusion chromosomes at the base of the 4th chromosome. The advantageous variant responsible for the establishment in frequency and maintenance of the X/4 fusion is thus inferred to be in the D. americana X centromere-inversion Xc basal breakpoint region.
authors.affiliation: Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal.
authors.forename: Cristina P
authors.initials: CP
authors.lastname: Vieira
authors.forename: André
authors.initials: A
authors.lastname: Almeida
authors.forename: João Daniel
authors.initials: JD
authors.lastname: Dias
authors.forename: Jorge
authors.initials: J
authors.lastname: Vieira
mesh_terms: D000818:Animals; D007446:Chromosome Inversion; D004330:Drosophila / Q000235:genetics*; D023061:Gene Order; D014644:Genetic Variation; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D011995:Recombination, Genetic; D012641:Selection, Genetic; D014178:Translocation, Genetic; D014960:X Chromosome