PREFACE 



In this book I have endeavored to state and to explain the 

 basic principles of biological inheritance and to show the impor- 

 tance of those principles to man, to the improvement of plants 

 and animals, and to organic evolution. I have attempted to pre- 

 sent this material in a simple fashion so that any reader can 

 grasp the fundamentals of heredity in spite of limited biological 

 training. However, I have also included some of the data that 

 support these principles so that the student who wishes can ac- 

 quire an adequate background for further studies in heredity, 

 and I have added a fairly extensive bibliography so that the 

 more serious student will have a diversified list of some of the 

 items of the research literature should he wish more information 

 on a subject than a book of this size can offer. 



Throughout this book I have stressed general principles rather 

 than practical applications and have drawn my illustrations 

 from both the Plant and the Animal Kingdoms. For the reader 

 who is interested in human biology, references to inherited traits 

 are numerous, and Chapters 3 and 19 should be of especial im- 

 portance. The emphasis on principles and the variety of the 

 illustrations should make this book of value to students of agri- 

 culture, psychology, and sociology. It should serve also as a 

 foundation for advanced work in genetics and cytogenetics. 



The book is readily divisible into four parts. The first five 

 chapters provide a survey of general biological information 

 which must be understood before progressing into the field of 

 genetics itself. In Chapters 6 through 13 I discuss the funda- 

 mental principles of the transmission of genes. In discussing the 

 method by which genes are distributed from generation to 

 generation, I have used the cytological approach, describing 

 chromosomes and their behavior at cell division and reproduc- 

 tion. Chapters 14 through 23 make up the third part of the 

 book. They deal with the nature and physiology of genes and 

 also include some topics of practical and of general interest. 



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