PREFACE vii 



students to mature scholars in disciplines other than genetics. It is writ- 

 ten out of an awareness tiiat genetics is rapidly becoming of keener interest 

 to scientists in other fields, as the impact of genetic determinants is felt in 

 their experiments, and to students in search of challenging research prob- 

 lems. It is written especially in the hope that for some readers the acqui- 

 sition of a broader understanding about a particular branch of science may 

 be an exhilarating intellectual experience. 



In preparing this book, we were aided by many friends and colleagues 

 who provided us generously with information, illustrations, and criticism. 

 We wish to acknowledge our deep appreciation to the following persons: 



C. B. Anfinsen, R. Appleyard, K. C. Atwood, H. Grouse, M. Demerec, 

 M. Fischberg, S. Fogel, P. E. Hartman, N. H. Horowitz, R. D. Hotchkiss, 

 J. lino, F. Gros, K. Kimura, J. Lederberg, E. B. Lewis, O. Maaloe, B. 

 McGlintock, G. E. Palade, D. D. Perkins, M. M. Rhoades, F. Stahl, J. H. 

 Taylor, M. Tsujita, H. Vogel, M. Westergaard. We are particularly in- 

 debted to S. Fogel, B. N. Jamin, and D. D. Perkins for their detailed 

 criticisms of the entire manuscript, and to G. E. Palade for the electron 

 micrographs. 



New York, RuTH SagER 



April 1961 Francis J. Ryan 



