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A novel sex-determining QTL in Nile tilapia (Oreochromis niloticus).

Palaiokostas C, Bekaert M, Khan MG, Taggart JB, Gharbi K, McAndrew BJ, Penman DJ - BMC Genomics (2015)

Bottom Line: Fish species often exhibit significant sexual dimorphism for commercially important traits.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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Stirling, FK9 4LA, Scotland, UK. c.palaiokostas@stir.ac.uk.

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.

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QTL mapping in family 1. Plots of the LOD score (sex-determining QTL search) along the linkage groups. Top graph, full dataset; bottom graph, reduced dataset (44 females and 21 males suspected to have undergone sex reversal). The numbers refer the linkage group numbers Table 3.
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Fig2: QTL mapping in family 1. Plots of the LOD score (sex-determining QTL search) along the linkage groups. Top graph, full dataset; bottom graph, reduced dataset (44 females and 21 males suspected to have undergone sex reversal). The numbers refer the linkage group numbers Table 3.

Mentions: QTL mapping for family 1 was conducted using R/qtl. The results from the single-QTL model for binary traits provided evidence for the existence of a QTL in LG 1, in the expected position of the major sex determining region (LOD = 9.65), and a second strong QTL in LG 20 (LOD = 4.87; Figure 2). The genome-wide significance threshold for the single-QTL model had a value of LOD = 2.77 (10,000 permutations; α = 0.05). Explained variances of the above QTLs were estimated after running a multi-dimensional QTL model. The QTL on LG 1 explained approximately 40.5% of the phenotypic variance (LOD = 15.13; P < 10−15), while the QTL on LG 20 explained approximately 25% of the phenotypic variance (LOD = 10.35; P < 10−11; Table 4).Figure 2


A novel sex-determining QTL in Nile tilapia (Oreochromis niloticus).

Palaiokostas C, Bekaert M, Khan MG, Taggart JB, Gharbi K, McAndrew BJ, Penman DJ - BMC Genomics (2015)

QTL mapping in family 1. Plots of the LOD score (sex-determining QTL search) along the linkage groups. Top graph, full dataset; bottom graph, reduced dataset (44 females and 21 males suspected to have undergone sex reversal). The numbers refer the linkage group numbers Table 3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4358704&req=5

Fig2: QTL mapping in family 1. Plots of the LOD score (sex-determining QTL search) along the linkage groups. Top graph, full dataset; bottom graph, reduced dataset (44 females and 21 males suspected to have undergone sex reversal). The numbers refer the linkage group numbers Table 3.
Mentions: QTL mapping for family 1 was conducted using R/qtl. The results from the single-QTL model for binary traits provided evidence for the existence of a QTL in LG 1, in the expected position of the major sex determining region (LOD = 9.65), and a second strong QTL in LG 20 (LOD = 4.87; Figure 2). The genome-wide significance threshold for the single-QTL model had a value of LOD = 2.77 (10,000 permutations; α = 0.05). Explained variances of the above QTLs were estimated after running a multi-dimensional QTL model. The QTL on LG 1 explained approximately 40.5% of the phenotypic variance (LOD = 15.13; P < 10−15), while the QTL on LG 20 explained approximately 25% of the phenotypic variance (LOD = 10.35; P < 10−11; Table 4).Figure 2

Bottom Line: Fish species often exhibit significant sexual dimorphism for commercially important traits.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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Aquaculture, School of Natural Sciences, University of Stirling, Stirling, FK9 4LA, Scotland, UK. c.palaiokostas@stir.ac.uk.

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.

Show MeSH
Related in: MedlinePlus