PREFACE 



to mention several qualities a general genetics 

 text should have and how the present text 

 attempts to meet these criteria. 



The text should be so organized that the 

 principles dealing with the nature of the 

 gene are separated as much as possible from 

 the applications or uses of these principles. 

 Too often students finish an elementary 

 course without a clear understanding of the 

 basic principles regarding genes, on the one 

 hand, and the consequences of these prin- 

 ciples, on the other. In the table of contents 

 all the Chapters containing either basic con- 

 cepts of the gene or information necessary 

 for the comprehension of basic concepts are 

 indicated by an asterisk, while Chapters 

 concerned entirely with the applications or 

 consequences of these basic principles are 

 not so marked. The marked Chapters deal- 

 ing with the nature of the gene include 

 all those which define, or delimit, the ge- 

 netic material operationally in terms of 

 its recombinational, mutational, functional, 

 chemical, and replicational properties, while 

 the other Chapters are concerned primarily 

 with the utilization of genetic principles for 

 the elucidation of problems in morphology 

 (traits), in development and physiology of 

 individuals, in populations, and in evolution. 

 While it would seem essential at one time 

 or another during the course to study many 

 or all the Chapters dealing with the nature 

 of the genetic material, any or all of the 

 Chapters concerning applications may be 

 omitted at the discretion of the instructor. 



A text should be used as a supplement to, 

 and not a substitute for, the teacher. It has 

 become impossible, as well as undesirable, 

 to include in one text how each principle 

 of genetics has been proven in the case of 

 every plant and animal studied. It is even 

 less possible to give examples of the applica- 

 tion of each of these principles to all the 

 diff'erent kinds of organisms. Accordingly, 

 in the present text only one or a few experi- 

 mentally favorable or historically important 



organisms are usually employed to establish 

 a principle or to illustrate an application. 

 Additional proofs, applications, or examples 

 are left to the instructor who, depending 

 upon his and his students' training and in- 

 terest, can supply other illustrations by 

 means of lectures and laboratory sessions or 

 by means of assignments to detailed accounts 

 in other texts and in the original literature. 

 A text, therefore, should be used to present 

 the fundamentals, while the instructor should 

 serve to clarify, amplify, coordinate, and 

 integrate them. There is Httle value in having 

 the student attend lectures in which all the 

 time is spent listening to the same material 

 that was discussed in the text. 



Since the study of the gene is an experi- 

 mental rather than a descriptive procedure, 

 the text should, whenever feasible, derive 

 the principles from the results of experiments. 

 The plan has been to build a solid structure 

 of genetic theory upon evidences and reason- 

 ing presented earlier or concurrently. Sen- 

 tences, paragraphs, section or chapter 

 headings, which state conclusions to be ar- 

 rived at sometime later in the text have been 

 avoided. In general the attempt has been 

 made to adhere as much as possible to the 

 following method of presentation: to recog- 

 nize a problem, offer evidence related to it, 

 analyze all reasonable explanations, and 

 draw whatever conclusions are warranted on 

 the basis of the information presented. Di- 

 gressions from the main purposes are avoided, 

 so, for example, a history of pregenetic 

 thought is not presented. 



Not the least value of a concise text is the 

 challenge the student may be given to utilize 

 the books and journals in the library. The 

 reading of genetic works in the original by 

 uninformed students is relatively unfruitful 

 for the effort expended, but may be a very 

 rewarding experience if done after reading 

 appropriate sections of the text. Accordingly 

 references requiring different degrees of so- 

 phistication are given at the ends of Chapters. 



