CONTENTS 



Chapter Page 



18 Development of Fertile Breeding Stocks 18-1 



Fermentative Characters 18-1 



Vitamin Deficiencies 18-3 



Haploid Non-Fermenters from a Weak Fer- 



menter by a Strong Fermenter Hybrid. . 18-5 



19 Regular Mendelian Inheritance 19-1 



A Gene -Controlled Adaptive Enzyme .... 19-1 



The Origin of a Nonfermenter of Galactose . 19-1 



Tetrad Analysis of ana G/ag Hybrid 19-1 



Mendelian Inheritance of Genes Affecting 

 Fermentative and Vitamin -Synthesizing 



Ability 19-4 



20 Irregular Ratios 20-1 



Non-Mendelian Inheritance of Ability to Fer- 

 ment Galactose 20-1 



Non-Mendelian Inheritance of Ability to 



Ferment Melibiose 20-4 



Irregular Ratios in Other Organisms .... 20-6 



The "Good Gene" Concept 20-7 



Graded Impairment of Gene Function .... 20-8 



21 The Effect of the Medium on Apparent Vitamin- 

 Synthesizing Deficiencies 21-1 



A Comparison of Two Synthetic Media. . . . 21-1 



The * Vitamin" Pedigree 21-3 



Hybrids between Yeasts Supposedly Differ- 

 ent in Vitamin -Synthesizing Ability . . . 21-4 

 Vitamin -Synthesizing Ability of Supposedly 



Deficient Yeasts in a Natural Medium. . 21-4 



Continuous Observation of Growth 21-4 



The Inadequacy of the Criterion, Equal 

 Increments of Growth for Equal Incre- 

 ments of Vitamin 21-6 



The Effect of Multiple Deficiencies of the 



B Vitamins 21-7 



The Relation between Viability of Cells 

 and Inability to Grow on Deficient 

 Medium 21-8 



22 The Separate Functions of Recessive and 

 Dominant Alleles in Adaptation to Pantothenate 

 Deficiency 22-1 



XV 



