PIEBALD RATS AND SELECTION AN EXPERIMENTAL TEST OF THE EFFECTIVENESS OF SELECTION AND OF THE THEORY OF GAMETIC PURITY IN MENDELIAN CROSSES BY W. E. CASTLE AND JOHN C. PHILLIPS [Illustration] WASHINGTON, D. C. PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON 1914 CARNEGIE INSTITUTION OF WASHINGTON, PUBLICATION NO. 195 PAPER NO. 21 OF THE STATION FOR EXPERIMENTAL EVOLUTION AT COLD SPRING HARBOR, NEW YORK FROM THE LABORATORY OF GENETICS OF THE BUSSEY INSTITUTION Copies of this Book were first issued FEB 18 1914 PRESS OF GIBSON BROTHERS, INC. WASHINGTON, D. C. CONTENTS. Page. Introduction 5 Material and methods 7 Plus selection series 9 Minus selection series 12 Return selection 13 Crosses with wild rats 16 Crosses with black “Irish” rats 18 Plus selection of “extracted hooded” rats 20 Crosses of the plus race with the minus race 22 Summary of results 22 Discussion 23 The “mutant” series 25 Bibliography 31 Tables 32-54 Explanation of plates 56 PIEBALD RATS AND SELECTION. INTRODUCTION. The fundamental importance of Mendel’s law of heredity is generally recognized among biologists. It is a working hypothesis whose utility is fully substantiated by abundant results daily increasing in amount. But biologists are not in agreement as to how much this law includes. All perhaps would agree that it implies the existence in the germ-cell of specific determiners essential for the production of particular characteristics in the offspring. Further, no one probably will object to the statement that it implies a dual or duplex condition of the zygote as regards determiners and a simple or simplex condition of the gamete. Thirdly, the fact will be admitted by all that most mendelizing characters are wholly independent of each other in heredity, for which reason we are forced to suppose that their determiners are distinct within the germ-cell.