Gene Variant of () Is Concordant with Female Determination in Cichlids.

fishes exhibit variability of sex-determination (SD) genes whose characterization contributes to understanding of the sex differentiation network, and to effective tilapia farming, which requires all-male culture. However, () is the only master-key regulator (MKR) of SD that has been mapped (XY/XX SD-system on LG23). In (), LG3 controls a WZ/ZZ SD-system that has recently been delimited to 9.2 Mbp, with an embedded interval rich with female-specific variation, harboring two genes and . Developing genetic markers within this interval and using a hybrid stock that demonstrates no recombination repression in LG3, we mapped the critical SD region to 235 Kbp on the orthologous physical map ( < 1.5 × 10). DNA-seq assembly and peak-proportion analysis of variation based on Sanger chromatograms allowed the characterization of copy-number variation (CNV) of . males had three exons capable of encoding 90-amino-acid polypeptides, yet in females, we found an extra copy with an 89-amino-acid polypeptide and three non-conservative amino acid substitutions, designated as CNV analysis suggested the existence of two to five copies of in diploidic Cichlidae. Disrupting the Hardy-Weinberg equilibrium ( < 4.2 × 10), was concordant with female determination in and in three cichlids with LG3 WZ/ZZ SD-systems (  and ). Furthermore, exclusive RNA-seq expression in females strengthened the candidacy of as the long-sought LG3 SD MKR. As genes mediate nuclear assembly, chromatin organization, gene expression and gonad development, may play a fundamental role inducing female nucleus formation that is essential for WZ/ZZ SD.