Genetics of Natural Populations. I. Chromosome Variation in Populations of Drosophila Pseudoobscura Inhabiting Isolated Mountain Ranges.

N RECENT years there appears to be a growing interest in the I genetics of free-living populations, a subject hitherto almost untouched. Certain species of Drosophila prove to be very suitable for investigations in this field. TSCHETWERIKOFF (CHETVERIKOV), DUBININ and their collaborators in Russia, TIMOFEEFF-RESSOVSKY in Germany, GORDON in England, and STURTEVANT in this country have secured much valuable information which opens new vistas and raises a host of new problems (for a short review of the literature see DOBZHANSKY 1937). It has seemed to us that a comparison of the genetic constitutions of several free-living popu' lations from the same general region, and yet isolated from each other, may be of interest. Samples of the populations of Drosophila pseudoobscura inhabiting island-like mountain forests in the Death Valley region of California and Nevada were collected. This region is especially favorable for our purposes, since it is as yet practically undisturbed by man's activities. We wish to acknowledge our obligations to Professor A. H. STURTEVANT for his valuable advice, to Mr. H. D. CURRY whose help enabled us to collect material in certain rather inaccessible localities, and to Messrs. G. T. RUDKIN and EDWARD HELD for their assistance in conducting the experiments.