Introduction

Abstract

In 1920 Detlefsen (29) published an article entitled “Is Crossing-over a function of distance?” Apparently this was not altogether approved of by Morgan’s school, for according to them Detlefsen did not quite grasp the true meaning of the chromosome maps, with the consequence that he underrated the research in connection with chromosome topography, for he stated: “We do not know that the distance which gives 1 % (or n %) of crossing-over is a fixed unit, .... our arbitrary unit of measurement may itself prove to be a variable”. He (Detlefsen) pointed out that he succeeded through selection experiments to reduce crossing-over in a certain case from 33 % to 0 %, in view of which consideration it would perhaps be simpler to conclude that linkage is not a function of distance, i.e. crossing-over is not necessarily proportional to distance. Detlefsen’s criticism was immediately answered by Sturtevant and others: “One unfamiliar with the literature of the subject would probably infer from Detlefsen’s paper that the possibility of inherited linkage variations had not been taken into account by those concerned in constructing chromosome maps. In point of fact, the matter has not only been taken into account, but has often been discussed in the literature ....”.