since reasoning reigns supreme here do not 

 look for a superfluity of visual material, 

 whose presence sometimes substitutes looking 

 for thinking. I suggest that you keep pencil 

 and paper handy so you can make your own 

 visual aids and provide yourself with ex- 

 perience in using the knowledge contained 

 here. Readers who already have some ideas 

 about genes should note that certain con- 

 cepts of the gene change during the course 

 of this book. At some earlier point in the 

 book the view of the gene may be quite dif- 

 ferent from the one commonly held and/or 

 different from the one presented later. Re- 

 tain an open mind. Be alert to those oc- 

 casions on which I shall draw incorrect 

 conclusions, or what at one point may seem 

 like a valid conclusion but which later, either 

 in this book or in tomorrow's discoveries, 

 proves to be only partially true or even 

 wrong. 



Suggestions for Use of the Book 



This book can be used several ways. It con- 

 tains more information than can be covered 

 in the usual one-semester introductory course 

 for undergraduates. 



A one-semester course (meeting about 31-45 



hours) can be based upon (1) the 31 Chapters 

 marked with asterisks, or (2) the first 35 

 Chapters, omitting at will certain unstarred 

 Chapters before Chapter 35, or (3) the fol- 

 lowing 24 Chapters: 1-4, 6, 31-49, supple- 

 mented as needed with several lectures on 

 material in unread Chapters. 



A tno-semester course (meeting a total of 

 about 60-90 hours) can be based upon the 

 first 30 Chapters the first semester and the 

 last 19 Chapters the second semester. Or, 

 the 31 Chapters with asterisks can be used 

 the first semester and the remaining 18 un- 

 starred Chapters the second. 



Making use of the Supplements and refer- 

 ence fists, for additional reading and dis- 

 cussion, the book can be used also in upper 

 class and graduate introductory genetics 

 courses. 



Acknowledgments 



Those figures for which credit is not otherwise 

 given were prepared by William J. Briggs. I 

 wish to thank my wife, Reida Postrel Her- 

 skowitz, for preparing the typescript. I am 

 especially indebted to my present and former 

 students for numerous suggestions. 



IRWIN H. HERSKOWITZ 



