Genetic contribution of parents in sex determination of honmoroko Gnathopogon caerulescens.

The honmoroko has been inferred to have an XX/XY sex determination system, but the parental genome can also affect the sex ratio of the offspring. The extent of parental effects on sex determination was examined by checking the sex ratios of F1 and F2 gynogenetic diploids and control diploids. Eleven gynogenetic broods from different females consisted of all or nearly all females, but eight broods showed a variable proportion of males (<50 %). One second-generation brood of gynogenetic diploids consisted wholly of females, but others produced some males. In crosses with a control diploid female, four males from a high-percentage male brood of gynogenetic diploids produced offspring with a balanced sex ratio. Sib-mating between a gynogenetic female and three gynogenetic males from the brood produced predominantly male progeny. These results suggest that there are at least four possible genotypes: genotypic female (XX), phenotypic female carrying a silent Y chromosome, genotypic male (XY), and genotypic supermale (YY). These inferences suggest that this fish has an XY system but a relatively high proportion of females possess a mutated, silent Y chromosome which does not lead to testis formation. [ABSTRACT FROM AUTHOR]