ILLUSTRATIONS xi 



59. Redistribution of genes in reproduction 285 



60. How parents showing many recessive, defec- 



tive characteristics may produce offspring 

 with none 292 



61. How parents showing no defects may pro- 



duce offspring with many defects 294 



62. Diagram showing different combinations re- 



sulting in the fourth generation 296 



63. Continuation of Figure 62 296 



64. Formation of trisomies 318 



65. Formation of a tetrasomic 320 



66. Different groups of chromosomes producing 



diverse types of organisms 323 



67. Method of formation of inversions, deletions 



and translocations 331 



68. Effect of an inversion at conjugation 333 



69. Chromosome groups in various different 



species related to Drosophila 337 



70. Relation of number of mutated genes to 



characteristic produced 357 



