Crossing-over between the X- and the Y-chromosome

Abstract

It is perhaps not too much to say that the absence of crossing-over between the X- and Y-chromosome of the male Drosophila really offers no problem for the simple reason that the morphological difference between the two chromosomes offers sufficient basis of explanation. But the cases that call for attention are especially those where either genetically or cytologically absence of crossing-over is not met with or not expected because of morphological and other reasons. Such cases as for instance crossing-over between the W- and the Z-chromosome of Platypoecilus, and crossing-over between the X and Y of Aplocheilus latipes and of Lebistes reticulatus, are cases we have in mind, especially because of the difference in frequency between the two directions of crossing-over.