title: Contrasting patterns of X/Y polymorphism distinguish Carica papaya from other sex chromosome systems.
abstract: The sex chromosomes of the tropical crop papaya (Carica papaya) are evolutionarily young and consequently allow for the examination of evolutionary mechanisms that drive early sex chromosome divergence. We conducted a molecular population genetic analysis of four X/Y gene pairs from a collection of 45 wild papaya accessions. These population genetic analyses reveal striking differences in the patterns of polymorphism between the X and Y chromosomes that distinguish them from other sex chromosome systems. In most sex chromosome systems, the Y chromosome displays significantly reduced polymorphism levels, whereas the X chromosome maintains a level of polymorphism that is comparable to autosomal loci. However, the four papaya sex-linked loci that we examined display diversity patterns that are opposite this trend: the papaya X alleles exhibit significantly reduced polymorphism levels, whereas the papaya Y alleles maintain greater than expected levels of diversity. Our analyses suggest that selective sweeps in the regions of the X have contributed to this pattern while also revealing geographically restricted haplogroups on the Y. We discuss the possible role sexual selection and/or genomic conflict have played in shaping the contrasting patterns of polymorphism found for the papaya X and Y chromosomes.
authors.affiliation: Department of Botany, Miami University, USA.
authors.forename: Laura A
authors.initials: LA
authors.lastname: Weingartner
authors.forename: Richard C
authors.initials: RC
authors.lastname: Moore
mesh_terms: D029441:Carica / Q000235:genetics*; D032461:Chromosomes, Plant / Q000235:genetics*; D003364:Costa Rica; D019143:Evolution, Molecular; D005828:Genetics, Population; D006239:Haplotypes / Q000235:genetics; D015810:Linkage Disequilibrium; D011110:Polymorphism, Genetic; D012641:Selection, Genetic; D012730:Sex Chromosomes / Q000235:genetics*; D012737:Sex Factors