title: A novel sex-determining QTL in Nile tilapia (Oreochromis niloticus).
abstract: BACKGROUND
  Fish species often exhibit significant sexual dimorphism for commercially important traits. Accordingly, the control of phenotypic sex, and in particular the production of monosex cultures, is of particular interest to the aquaculture industry. Sex determination in the widely farmed Nile tilapia (Oreochromis niloticus) is complex, involving genomic regions on at least three chromosomes (chromosomes 1, 3 and 23) and interacting in certain cases with elevated early rearing temperature as well. Thus, sex ratios may vary substantially from 50%.
  
  
  RESULTS
  This study focused on mapping sex-determining quantitative trait loci (QTL) in families with skewed sex ratios. These included four families that showed an excess of males (male ratio varied between 64% and 93%) when reared at standard temperature (28°C) and a fifth family in which an excess of males (96%) was observed when fry were reared at 36°C for ten days from first feeding. All the samples used in the current study were genotyped for two single-nucleotide polymorphisms (rs397507167 and rs397507165) located in the expected major sex-determining region in linkage group 1 (LG 1). The only misassigned individuals were phenotypic males with the expected female genotype, suggesting that those offspring had undergone sex-reversal with respect to the major sex-determining locus. We mapped SNPs identified from double digest Restriction-site Associated DNA (ddRAD) sequencing in these five families. Three genetic maps were constructed consisting of 641, 175 and 1,155 SNPs from the three largest families. QTL analyses provided evidence for a novel genome-wide significant QTL in LG 20. Evidence was also found for another sex-determining QTL in the fifth family, in the proximal region of LG 1.
  
  
  CONCLUSIONS
  Overall, the results from this study suggest that these previously undetected QTLs are involved in sex determination in the Nile tilapia, causing sex reversal (masculinisation) with respect to the XX genotype at the major sex-determining locus in LG 1.
authors.affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Stirling, FK9 4LA, Scotland, UK. c.palaiokostas@stir.ac.uk.
authors.forename: Christos
authors.initials: C
authors.lastname: Palaiokostas
authors.affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Stirling, FK9 4LA, Scotland, UK. m.bekaert@stir.ac.uk.
authors.forename: Michaël
authors.initials: M
authors.lastname: Bekaert
authors.affiliation: Department of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh, Bangladesh. khanmgq@yahoo.com.
authors.forename: Mohd G Q
authors.initials: MG
authors.lastname: Khan
authors.affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Stirling, FK9 4LA, Scotland, UK. j.b.taggart@stir.ac.uk.
authors.forename: John B
authors.initials: JB
authors.lastname: Taggart
authors.affiliation: Edinburgh Genomics, Ashworth Laboratories, King's Buildings, University of Edinburgh, Edinburgh, EH9 3JT, Scotland, UK. Karim.Gharbi@ed.ac.uk.
authors.forename: Karim
authors.initials: K
authors.lastname: Gharbi
authors.affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Stirling, FK9 4LA, Scotland, UK. b.j.mcandrew@stir.ac.uk.
authors.forename: Brendan J
authors.initials: BJ
authors.lastname: McAndrew
authors.affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Stirling, FK9 4LA, Scotland, UK. d.j.penman@stir.ac.uk.
authors.forename: David J
authors.initials: DJ
authors.lastname: Penman
mesh_terms: D000818:Animals; D002874:Chromosome Mapping; D023681:Cichlids / Q000235:genetics*; D005260:Female; D008297:Male; D020641:Polymorphism, Single Nucleotide; D040641:Quantitative Trait Loci; D017422:Sequence Analysis, DNA; D019849:Sex Determination Processes; D012744:Sex Ratio; D013696:Temperature