title: Sex determination in the genus Oreochromis : 1. Sex reversal, gynogenesis and triploidy in O. niloticus (L.).
abstract: Established techniques of genetic manipulation were used to elucidate sex-determining mechanisms in the commercially important tilapia, Oreochromis niloticus. Analysis of sex ratios from single-pair matings of normal broodstock showed these to be heterogeneous, with an asymmetrical frequency distribution. Data were homogeneous, with the exclusion of a number of broods with sex ratios not significantly different from 3∶1 (male: female), and further progeny testing revealed atypical female heterogamety in the parents of these broods. Analysis of sex ratios from complete diallele-type crosses using five males and five females demonstrated no association between male parent, female parent and progeny sex ratio. Sex ratios of gynogens (0∶1) and triploids (1∶1), and from progeny testing of sex-reversed males (0∶1) and sex-reversed females (3∶1), provide evidence for female homogamety in this species. Progeny testing of male gynogens derived from sex-reversed females demonstrated recombination between the centromere and the sex-determining locus (68.9%). Novel YY "supermales" were shown to be viable and produced all-male offspring. It was concluded that this species exhibits monofactorial, genotypic sex determination with male heterogamety. However, rare autosomal or environmental sex-modifying factors may account for occasional deviations from expected sex ratios.
authors.affiliation: School of Biological Sciences, University College of Swansea, SA2 8PP, Swansea, UK.
authors.forename: G C
authors.initials: GC
authors.lastname: Mair
authors.forename: A G
authors.initials: AG
authors.lastname: Scott
authors.forename: D J
authors.initials: DJ
authors.lastname: Penman
authors.forename: J A
authors.initials: JA
authors.lastname: Beardmore
authors.forename: D O
authors.initials: DO
authors.lastname: Skibinski