On the occurrence ofXX males inLebistes, with some remarks on aida’s so-called “Non-disjunctional” males inAplocheilus

Summary

In certainLebistes races the females (XX) are apt to show male characters and develop colour, though normally only males (XY) show colour patterns. By appropriate crossings of such races it proved possible to produce a fewXX males. Such males mated with normal females gave only females; through inbreeding it is possible to produce individuals again which are more or less altered in a male direction.

These experiments show that, although genes in theX-Y-chromosome pair normally are alone decisive as regards sex, it is possible through selection to produce types in which other chromosomes take over the sex determination. They show also that bothX-chromosomes and autosomes contain genes which have a share in the sex determination.

The remarkable fact that the closely relatedPlatypoecilus has homogametic males and heterogametic females is explained on the ground that the sex determination is of a quantitative nature, so that the heterogamety may change from being a male to being a female characteristic.

Aida’s so-called non-disjunctional males inAplocheilus (1930), which in like manner produce nearly all females, must be regarded, not as having arisen through non-disjunction, in which case they should containXXY, but as beingXX males.