Sex determination in the genus Oreochromis |
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Authors: | G C Mair A G Scott D J Penman D O F Skibinski J A Beardmore |
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Institution: | (1) School of Biological Sciences, University College of Swansea, SA2 8PP Swansea, UK;(2) Present address: FAC/CLSU-UCS Tilapia Genetics Project, Freshwater Aquaculture Center, Central Luzon State University, 3120 Munoz, Nueva Ecija, The Philippines;(3) Present address: Department of Pure and Applied Biology, University of Reading, Aquatic Biology Research Unit, P.O. Box 228, RG6 2AJ Reading, Berkshire, UK;(4) Present address: Institute of Aquaculture, University of Stirling, FK9 4LA Stirling, Scotland, UK |
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Abstract: | Summary Sex ratios from 62 single-pair matings of normal broodstock O. aureus were highly heterogeneous with an overall deficit of males (41.4%). Peaks in the sex ratio frequency distribution occurred at 1 1, 3 5 and 1 3 (male female). Hybridisation of O. aureus with O. mossambicus, O. spilums and O. niloticus produced highly variable sex ratios, suggesting a complexity of hybrid sex determination. Few valid inferences could be made regarding intraspecific sex determination from these hybrid data. Sex ratios from progeny testing of sex-reversed males (1 3) and most sex-reversed females (1 0) provide evidence for female heterogamety in O. aureus. Several aberrant ratios observed suggest Mendelian inheritance of an autosomal recessive gene (F,f), epistatic to the major sex-determining gene (W,Z). Sex ratios of triploids and gynogens support the hypothesis of recombination between the centromere and the major sex-determining locus. Progeny testing of a female mitogyne demonstrated the viability of a novel WW superfemale , which gave only female offspring. Not all data could be explained by a two-factor model of sex determination. Further exceptional sex ratios may be accounted for by rare autosomal or environmental sex-modifying factors. It is concluded that O. aureus has a multifactorial mechanism of sex determination with the underlying primary mechanism of female heterogamety. |
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Keywords: | Sex determination Oreochromis aureus Gynogenesis Sex reversal Hybridisation |
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