title: Genomic structures of the kW1 loci on the Z and W chromosomes in ratite birds: structural changes at an early stage of W chromosome differentiation.
abstract: The W chromosome of ratite birds shows minimal morphological differentiation and retains homology of genetic linkage and gene order with a substantial stretch of the Z chromosome; however, the molecular structure in the differentiated region is still not well known. The kW1 sequence was isolated from the kiwi as a W-specific DNA marker for PCR-based molecular sexing of ratite birds. In ratite W chromosomes, this sequence commonly contains a ∼200-bp deletion. To characterize the very early event of avian sex chromosome differentiation, we performed molecular cytogenetic analyses of kW1 and its flanking sequences in paleognathous and neognathous birds and reptiles. Female-specific repeats were found in the kW1-flanking sequence of the cassowary (Casuarius casuarius), and the repeats have been amplified in the pericentromeric region of the W chromosomes of ratites, which may have resulted from the cessation of meiotic recombination between the Z and W chromosomes at an early stage of sex chromosome differentiation. The presence of the kW1 sequence in neognathous birds and a crocodilian species suggests that the kW1 sequence was present in the ancestral genome of Archosauria; however, it disappeared in other reptilian taxa and several lineages of neognathous birds.
authors.affiliation: Laboratory of Animal Cytogenetics, Department of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Ishijima
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Uno
authors.forename: Chizuko
authors.initials: C
authors.lastname: Nishida
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Matsuda
mesh_terms: D000489:Alligators and Crocodiles / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D002874:Chromosome Mapping; D019143:Evolution, Molecular; D005260:Female; D008297:Male; D008969:Molecular Sequence Data; D046108:Palaeognathae / Q000235:genetics*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D012730:Sex Chromosomes / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics
chemical_list: C110547:DMRT1 protein; D014157:Transcription Factors