Subject Index 



593 



Secale cereale, 525 

 Secondary association, 468, 469 

 Segmental interchange, 203 

 Segregation, law of, 82 



of genes in autotetraploids, 448 

 Selection, 367 ff., 538, 539 



and plant and animal breeding, 

 376, 377, 378, 379, 380, 381, 

 382, 383 

 elimination of spontaneous le- 



thals by, 255 

 isolation of biotypes by, 379 

 within pure lines, 371 

 Self-fertility, 277 

 Self-fertilization, 66, 85, 86, 368, 369, 



371 

 Self-incompatibility, 271, 272 

 Self-sterility, 271, 272, 273, 274, 275, 



276, 277 

 Self-sterility alleles, linkage of with 

 other genes, 274, 275, 276, 277, 

 353 

 Semi-sterile plants, 406, 407, IfOS 

 Setcreasia brevifolia, 448 

 Sex chromosomes, 68 ff., 513 

 heteropycnosis of, 486, 487, JfS8 

 ratio of to autosomes, 482, 483, 

 506, 507 

 Sex inheritance, 68 ff.. 480 ff. 

 attached-X stocks, 249, 483 

 balance theory of, 481-485, 486, 



493 

 female-determining substance, 484, 



493 

 hormones and, 494, 495 

 importance of environment on, 



495 

 in plants, 73, 502-514 

 male-determining substance, 484, 



493 

 potentialities for either sex, 493 

 probability of a male, 109, 110, 



111 

 sex-gene suppressors, 485 

 strong and weak races, 484 

 XO type, 69, 70, 134, 481, 505 

 XY type, 68, 69, 481, 505, 506 

 ZW type, 69, 70, 481, 505 



Sex linkage, incomplete, 95, 106, 

 196, 197 



in plants, 101-103 



XY and XO types, 95, 97, 98 



ZW and ZO types, 98, 99 

 Sex-linked lethals, mutation rate of, 



240, 261 

 Sex reversal, 483, 484, 494 

 Sheep, Cotswold, 90 



Dorset, 87, 88, 90, 91, 92 



horns in, 87, 90, 91, 92 



Merino, 90, 91, 92 



multiple alleles in, 90, 91, 92 



Rambouillet, 90, 91 



Shropshire, 90 



Southdown, 90 



Suffolk, 88, 90 

 Silkworm, failure of chiasma for- 

 mation in females, 154, 167, 

 213 

 Simplex, 448, 462 

 Single nature of chromosomes, 52, 



53 

 Size, in polyploids, 449, 450, 4-51 

 Size genes, 342 ff., 367 ff. 

 Snail, 318, 319, 523 

 Snapdragon, 323. 450 

 Solenobia, tetraploids of, 450 

 Soma, 225, 489. 503, 504 

 Somatic cros.sing over. 216, 217, 235 

 Somatic mutation, 233, 235, 238, 



258, 259, 374 

 Somatic nondisjunction, 429, 430 

 Somatic pairing in Diptera, 214, 



216 

 Somatoplastic sterility. 525 

 Sorghum, haploids, 435, 437 

 Spartina, 457, 458 

 Speciation, 227, 530, 531, 533 

 Species concept, 516, 517, 526, 528 

 Sperm, inactivated, 253 

 Sperm nucleus. 51, 52, 442, 443 

 Spermatids, 49, 503, 504 

 Spermatocytes, 49, 65, 72, 434, 486, 



491 

 Spermatozoon, 48, 49, 66, 68, 69. 70, 



434, 503, 504 

 Spiders, 522, 523 



