PREFACE 



S 



Iince the beginning of this cen- 

 tury the science of genetics 

 has had a spectacular growth. 

 The discovery of basic principles and the 

 application of these principles are occurring 

 at an ever-increasing rate. It is generally 

 agreed that a knowledge of genetics is essen- 

 tial for an understanding of present and fu- 

 ture biology. The impact of genetics is not 

 restricted, however, to professional teachers 

 and research workers in pure and applied 

 biology, nor to physicians and dentists. 

 More and more students whose major in- 

 terest is in psychology, biochemistry, chem- 

 istry, biophysics, physics, or mathematics 

 find that the study of genetics offers new and 

 challenging opportunities in these various 

 fields. 



How can a text for an introductory course 

 in genetics be best organized to serve stu- 

 dents with such varied interests? An intro- 

 ductory text must provide the reader with an 

 understanding of the nature of the genetic 

 material, for this knowledge is a prerequisite 

 for a fruitful genetic approach to the solution 

 of problems in biology and all the other 

 fields mentioned. Accordingly, insofar as 

 possible, the subject matter of this book is 

 arranged so that principles dealing with the 

 nature of the genetic material are separated 

 from the applications of these principles. 

 The nature of the genetic material is studied 

 through the use of the operations or methods 

 of recombination, mutation, chemistry and 

 physics, replication, and function. The pres- 

 entation is designed to encourage the reader 

 to use his powers of inductive reasoning to 

 arrive at the primary generalizations of 



genetics on the basis of experimental evi- 

 dence. Whenever feasible, genetic principles 

 are derived scientifically — by recognizing 

 and stating a problem, designing appropriate 

 experiments to test hypotheses, analyzing the 

 experimental results, and drawing conclu- 

 sions. The aim is to present genetics as a 

 rational, organized body of knowledge. 



Because of its importance the introductory 

 genetics course is being offered more fre- 

 quently in the earlier rather than the later 

 years of college study. Since such a course 

 is elected more and more frequently by 

 students who do not wish to specialize in 

 biology, simple biological examples and ter- 

 minology are used whenever possible, and 

 certain biological phenomena generally un- 

 derstood by students specializing in biology 

 are explained in some detail. Because many 

 students in a first course in genetics may not 

 have an adequate background, certain as- 

 pects of chemistry and physics important 

 for understanding genetics are described in 

 greater detail than in other texts. 



No single text can include the ways each 

 principle of genetics apply to every plant 

 and animal studied, or give examples of the 

 application of each of these principles to all 

 the different kinds of organisms. Accord- 

 ingly, only one or a few experimentally 

 favorable or historically important organisms 

 are usually employed in this text to establish 

 a principle or to illustrate an application. 

 Additional proofs, applications, or examples 

 are left to the instructor who, depending 

 upon his students' training and interest, can 

 supply other illustrations by means of lec- 

 tures and laboratory sessions or by means 

 of assignments to detailed accounts in other 

 texts and in the original literature. 



It is hoped that the text will stimulate 

 readers to utilize the books and journals in 

 their libraries. The reading of genetic works 

 in the original after studying appropriate 

 sections of the text can be a very rewarding 

 experience. Accordingly, references requir- 



