title: A primitive Y chromosome in papaya marks incipient sex chromosome evolution.
abstract: Many diverse systems for sex determination have evolved in plants and animals. One involves physically distinct (heteromorphic) sex chromosomes (X and Y, or Z and W) that are homozygous in one sex (usually female) and heterozygous in the other (usually male). Sex chromosome evolution is thought to involve suppression of recombination around the sex determination genes, rendering permanently heterozygous a chromosomal region that may then accumulate deleterious recessive mutations by Muller's ratchet, and fix deleterious mutations by hitchhiking as nearby favourable mutations are selected on the Y chromosome. Over time, these processes may cause the Y chromosome to degenerate and to diverge from the X chromosome over much of its length; for example, only 5% of the human Y chromosome still shows X-Y recombination. Here we show that papaya contains a primitive Y chromosome, with a male-specific region that accounts for only about 10% of the chromosome but has undergone severe recombination suppression and DNA sequence degeneration. This finding provides direct evidence for the origin of sex chromosomes from autosomes.
authors.affiliation: Hawaii Agriculture Research Center, Aiea, Hawaii 96701, USA.
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Liu
authors.forename: Paul H
authors.initials: PH
authors.lastname: Moore
authors.forename: Hao
authors.initials: H
authors.lastname: Ma
authors.forename: Christine M
authors.initials: CM
authors.lastname: Ackerman
authors.forename: Makandar
authors.initials: M
authors.lastname: Ragiba
authors.forename: Qingyi
authors.initials: Q
authors.lastname: Yu
authors.forename: Heather M
authors.initials: HM
authors.lastname: Pearl
authors.forename: Minna S
authors.initials: MS
authors.lastname: Kim
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Charlton
authors.forename: John I
authors.initials: JI
authors.lastname: Stiles
authors.forename: Francis T
authors.initials: FT
authors.lastname: Zee
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Paterson
authors.forename: Ray
authors.initials: R
authors.lastname: Ming
mesh_terms: D000483:Alleles; D001483:Base Sequence; D029441:Carica / Q000235:genetics*; D032461:Chromosomes, Plant / Q000235:genetics*; D003001:Cloning, Molecular; D020451:Contig Mapping; D012734:Disorders of Sex Development / Q000235:genetics; D019143:Evolution, Molecular; D017343:Genes, Plant / Q000235:genetics; D005819:Genetic Markers; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D019849:Sex Determination Processes; D014998:Y Chromosome / Q000235:genetics*
chemical_list: D005819:Genetic Markers