Ricerche sulla determinazione del sesso nel CopepodeTisbe gracilis(T. Scott)

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Abstract
In the Copepod Tisbe gracilis sex-ratio is highly variable in the different families. The results of experiments of inbreeding, outbreeding, selection towards increase of males and towards increase of females, arc reported in the present paper. Inbreeding leads to an increase of males, outbreeding to an increase of females. Selection, when carried out under inbreeding, is effective only in the direction towards males. Some preliminary results show that selection, when carried out without inbreeding, is effective in bolli directions. Crosses between inbred lines previously selected towards increase of males for some generations are followed by an increase in the number of females, though not so high as that observed in the experiments of outbreeding. The above results suggest that selection has operated upon a system of polygenes controlling sexuality. In Tisbe gracilis, beside the action of specific multiple factors for maleness and femaleness, also the factor « degree of heterozygosity » plays an important role. Its mechanism, however, remains to be clarified.

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