An investigation of sex determination in the Mozambique tilapia, Oreochromis mossambicus, using synaptonemal complex analysis, FISH, sex reversal and gynogenesis

The Mozambique tilapia, Oreochromis mossambicus, is known to have an XX female/XY male sex determination system. Analysis of the pachytene meiotic chromosomes in O. mossambicus and hybrids with Oreochromis niloticus demonstrated a region of diffuse lateral elements and differential staining in the long arm of bivalent I that was present only in heterogametic fish. Homology was also demonstrated between the chromosome pair 1 of O. niloticus (which has been previously demonstrated to be the sex chromosomes) and the same chromosome pair of O. mossambicus through fluorescent in situ hybridisation using probes prepared from the O. niloticus chromosome 1. This suggests that chromosomes in pair I are the sex chromosomes of the Mozambique tilapia. Meiotic gynogenetic progeny from O. mossambicus XY neofemales consisted of both YY and XY males but no females, in contrast to a previous study in which only YY male and XX female meiotic gynogenetics were produced in similar experiments. Autosomal genetic effects on sex determination were detected for the first time in this species. (C) 2003 Elsevier Science B.V. All rights reserved.