CONTENTS 



INTRODUCTION 1 



PART I: 



THE NATURE OF THE GENETIC MATERIAL 



1. The Chromosome and Its Division 6 



2. Genie and Non-genie Parts of the Chromosome 18 



A. Conclusions from Morphology 18 



B. Conclusions from Biochemistry 25 



a. Chemistry of the Chromosome 25 



b. DNA as Genie Material 31 

 aa. Quantitative Constancy of DNA 31 

 bb. Information Derived from the Structure of the 



Nucleic Acid Molecule 35 



cc. Conclusions from Bacterial Transformation and 



Transduction 47 



dd. Some Additional Relevant Facts 53 



c. Ceneral Conclusions 56 



C. Heterochromatin 57 



a. The Cytological Aspect 57 



b. Chromatin Diminution and Related Phenomena 60 



c. Interpretations Derived from tlie Cytological Facts 66 



d. Cytology and Genetics of Heterochromatin in DrosophiJa 70 

 aa. Chromocentric and Y-Chromosomal Heterochromatin 71 

 bb. Genetic Functions? Chromosomal Breaks and Het- 

 erochromatin 77 



cc. Intercalary Heterochromatin 83 



dd. Genetic Function of Intercalary Heterochromatin 85 



ee. Heterochromatin and the Genetics of Sex 90 



3. Chromosomes and Genes 95 



A. The Theory of the Gene 96 



B. The Theory of the Gene Molecule 100 



a. Treffer Theory 100 



b. Return Mutation 105 



c. Counting the Genes 107 



vii 



lid^l 



