ADVANCES IN GENETICS VOLUME 16 Edited by E. W. CASPARI Department of Biology University of Rochester Rochester, New York 1971 ACADEMIC PRESS NEW YORK AND LONDON COPYRIGHT 0 1971, BY ACADEMIC PRESS, INC. ALL RIGHTS RESERVED NO PART OF THIS BOOK MAY BE REPRODUCED IN A N Y FORM, BY PHOTOSTAT, MICROFILM, RETRIEVAL SYSTEM, OR ANY OTHER MEANS, WITHOUT WR-N PERMISSION FROM THE PUBLISHERS. ACADEMIC PRESS, INC. 111 Fifth Avenue, New York, New York 10003 United Kingdom Edition published by ACADEMIC PRESS INC. (LONDON) LTD. 24/28 Oval Road, Londoi NWl IDD LIBRARY OF CONGRESS CATALOQ CARD NUMBER:47-30313 PRINTED IN THE UNITED STATES OF AMERICA DEDICATION M. Demerec Editor of Advances in Genetics About two years ago, I was approached by some of his former collaborators with the suggestion to dedicate a volume of Advances in Genetics to the memory of M. Demerec. I gladly accepted this proposal since it seems to me fitting that Advances in Genetics honor in this way the memory of its founder and the Editor of its first nine volumes. Demerec became concerned about the “information explosion” in the sciences long before it became a popular topic of complaint. H e was possibly more aware than others of the resulting lack of communication between scientists in different though related fields, because he himself refused to be confined by artificial boundaries, and changed the object of his research several times in his life. H e had thus to get acquainted with new techniques and with a completely new literature. Part of his prodigious energy was therefore devoted to various means by which communication between scientists active in different fields could be established and extended. The founding of Advances in Genetics was one of his main activities in this direction. It was particularly designed to make it possible for geneticists working in a particular area and with a particular organism to get acquainted with work done in other fields of genetics. H e writes in the Preface to Volume I (1947): This series of review articles, Advances in Genetics, has been started in order that critical summaries of outstanding genetic problems, written by competent geneticists, may appear in a single publication.The articles are expected to deal with both theoretical and practical problems, and to cover plant breeding, animal breeding, and human heredity, as well as the related fields of biophysics, biochemistry, physiology, and immunology. The aim is to have the articles written in such form that they will be useful as reference material for geneticists and also as a source of information to nongeneticists. The way these stated goals were implemented can be seen from the contents of the volumes which appeared under Demerec’s editorship. They have continued to serve as guidelines for the editorial policies of Advances in Genetics. Y vi DEDICATION The review papers contained in this volume have been prepared by friends and former collaborators of Demerec. They reflect, therefore, to a certain degree, his interests during the last half of his scientific life. But since his interests were always wide ranging, and encompassed the whole range of genetics, the articles contained in this volume are not much more uniform than those in other volumes of this series. We hope that this volume constitutes a fitting memorial to a great geneticist who, by his own work, and by stimulating and facilitating the work of other scientists, has deeply influenced the direction genetics has taken in the last twenty years, and has contributed greatly to the conspicuous progress of genetics during his lifetime. I want to thank sincerely those geneticists who, by their contributions to this volume or by service on the Editorial Committee, have helped to make the ap