CONTENTS 



PAGE 



CHAPTER 



f I. Introduction 15 



II. Mendel's First Law — Segregation of the Genes 19 



' III. The Mechanism of Segregation 39 



IV. Mendel's Second Law — The Independent Assortment of 



the Genes 59 



V. The Mechanism of Assortment 73 



VI . Linkage 80 



VII . Crossing Over 87 



VIII. Crossing Over and Chromosomes 96 



IX. The Order of the Genes 118 



/ X. Interference 126 



XI. Limitation of the Linkage Groups 133 



XII. Variation in Linkage 139 



XIII. Variation in the Number of the Chromosomes and its Re- 



lation TO THE Totality of the Genes 147 



XIV. Sex-Chromosomes and Sex-lenked Inheritance 165 



XV. Parthenogenesis and Pure Lines 204 



XVI. The Embryological and Cytological Evidence that the 



Chromosomes are the Bearers of the Hereditary Units . . 212 



XVII. Cytoplasmic Inheritance 219 



XVIII. Maternal Inheritance 227 



XIX. The Particulate Theory of Heredity and the Nature of 



the Gene 234 



XX. Mutation 247 



