In contrast to mammals and birds,fish display an amazing diversity of genetic sex determination systems,with frequent changes during evolution possibly associated with theemergence of new sex chromosomes and sex-dete...
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In contrast to mammals and birds,fish display an amazing diversity of genetic sex determination systems,with frequent changes during evolution possibly associated with the emergence of new sex chromosomes and sex-determining *** better understand the molecular and evolutionary mechanisms driving this diversity,several fish models are studied in *** the medaka(Oryzias latipes Temminck and Schlegel,1846)for which the master sex-determination gene has been identified,one of the most advanced models for studying sex determination is the Southern platyfish(Xiphophorus maculatus,Günther 1966).Xiphophorus maculatus belongs to the Poeciliids,a family of live-bearing freshwater fish,including platyfish,swordtails and guppies that perfectly illustrates the diversity of genetic sex-determination mechanisms observed in *** ***,bacterial artificial chro-mosome contigs covering the sex-determination region of the X and Y sex chromosomes have been *** molecular analysis demonstrated that the sex-determination region is very unstable and frequently undergoes duplications,deletions,inversions and other *** gene candidates linked to the master sex-determining gene have been identified,some of them corresponding to *** putative genes are present on both the X and the Y chromosomes,suggesting a poor degree of differentiation and a young evolutionary age for platyfish sex *** compared with other fish and tetrapod genomes,syntenies were detected only with *** observation supports an independent origin of sex chromosomes,not only in different vertebrate lineages but also between different fish species.
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