Crossing-over between theX- and theY-chromosome inLebistes

Résumé

A factore (elongatus), involving an elongated caudal fin in male individuals ofLebistes reticulatus, shows sex-linked inheritance, for which reason thee-factor must have its seat in theX-chromosome of the male.

Crossing-over between theX- and theY-chromosome is recorded, thee-factor thereby being transferred from theX-chromosome to theY-chromosome. Males having thus theire-factor in theY-chromosome, show one-sided male inheritance of the elongated tail fin.

In these cross-over males, having thee-factor in theY-chromosome, a new crossing-over may take place betweenX andY, so that thee-factor returns to theX-chromosome, and so on. The mode of inheritance is therefore continually oscillating between sex-linked inheritance and one-sided male inheritance.

The above shows that theX- and theY-chromosome inLebistes respectively contain a dominant male sex-factor and a recessive female sex-factor; also that this pair of factors is entirely like other pairs because its location in the chromosome is certain, and because it shows linkage to colour-factors, crossing-over, etc. In the above respects, the divergence from conditions inDrosophila melanogaster is rather striking.

The Presence-Absence Theory and an ideal terminology are discussed.