Mapping and validation of the major sex-determining region in Nile tilapia (Oreochromis niloticus L.) Using RAD sequencing

PLoS One. 2013 Jul 11;8(7):e68389. doi: 10.1371/journal.pone.0068389. Print 2013.

Abstract

Sex in Oreochromis niloticus (Nile tilapia) is principally determined by an XX/XY locus but other genetic and environmental factors also influence sex ratio. Restriction Associated DNA (RAD) sequencing was used in two families derived from crossing XY males with females from an isogenic clonal line, in order to identify Single Nucleotide Polymorphisms (SNPs) and map the sex-determining region(s). We constructed a linkage map with 3,802 SNPs, which corresponded to 3,280 informative markers, and identified a major sex-determining region on linkage group 1, explaining nearly 96% of the phenotypic variance. This sex-determining region was mapped in a 2 cM interval, corresponding to approximately 1.2 Mb in the O. niloticus draft genome. In order to validate this, a diverse family (4 families; 96 individuals in total) and population (40 broodstock individuals) test panel were genotyped for five of the SNPs showing the highest association with phenotypic sex. From the expanded data set, SNPs Oni23063 and Oni28137 showed the highest association, which persisted both in the case of family and population data. Across the entire dataset all females were found to be homozygous for these two SNPs. Males were heterozygous, with the exception of five individuals in the population and two in the family dataset. These fish possessed the homozygous genotype expected of females. Progeny sex ratios (over 95% females) from two of the males with the "female" genotype indicated that they were neomales (XX males). Sex reversal induced by elevated temperature during sexual differentiation also resulted in phenotypic males with the "female" genotype. This study narrows down the region containing the main sex-determining locus, and provides genetic markers tightly linked to this locus, with an association that persisted across the population. These markers will be of use in refining the production of genetically male O. niloticus for aquaculture.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chromosome Mapping / methods
  • Cichlids / genetics*
  • Female
  • Genetic Linkage
  • Genetic Markers / genetics
  • Genotype
  • Heterozygote
  • Homozygote
  • Male
  • Polymorphism, Single Nucleotide / genetics
  • Sequence Analysis, DNA / methods
  • Sex Determination Processes / genetics*
  • Sex Differentiation / genetics*
  • Sex Ratio

Substances

  • Genetic Markers

Grant support

The authors are grateful for support from the Marine Alliance for Science and Technology for Scotland, a Commonwealth PhD scholarship to MGQK (CSC reference BDCS-2007-28), and University of Stirling PhD scholarship to CP. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.