CONTENTS II 



CHAPTER ^^^^ 



V. The Mechanics of the Chromosomes 113 



1. The relation of meiosis and mitosis 113 



2. Chiasmata 118 



3. The theory of crossing-over 121 



4. Chiasma interference 125 



5. Other theories of crossing-over and chiasma formation 126 



6. Compound crossing-over and chromatid interference 128 



7. Crossing-over in structural hybrids 129 



8. The cause of crossing-over 131 



PART TWO 



GENETICS AND DEVELOPMENT 



VI. Genes and Development 137 



1. The equal division of the nucleus I37 



2. General concepts of developmental mechanics 139 



3. Mosaic eggs I4i 



4. Insects 143 



5. Echinoderms ^45 



6. Amphibia 148 



7. Other vertebrates 152 



8. Acetabularia 152 



9. Development as an epigenetic process 154 

 10. Substance genes and pattern genes 156 



VII. The Interaction of Genes: The Effects 158 



1. Allelomorphs and multiple factors 158 



2. Epistasis ^^^ 



3. Suppressors ^^° 



4. Modifying factors 161 



5. Multiple effeas of a factor or pleiotropy 162 



