CONTENTS 



Paoi 



Preface v 



I. [introduction ! 



II. The Mutated Gene \m> the Potentialities of Development 3 



1. The phenocopies 4 



A. Description 4 



B. Related phenomena 10 



C. The sensitive period 13 



D. Combination effect of gene and phenocopy 22 



2. The phenocopies and the development of mutants 23 



A. Facts of mutant development 23 



B. Mutant character and developmental stage 39 



C. Lethality 42 



D. Preliminary conclusions 44 



E. Some pertinent facts from experimental embryology . ... 46 



3. The mutant gene and the rate concept 51 



A. Rate genes 52 



B. General experimental evidence 56 



1. A typical case 56 



2. The threshold concept 65 



3. Penetrance 69 



4. Further evidence 72 



4. Some special types of mutant genes and genie actions 78 



A. Pleiotropy 78 



B. Multiple alleles 81 



C. Genes controlling known chemical processes 90 



5. The gene in heterozygous state 99 



A. The influence of the environment upon dominance .... 102 



B. Dominigenes 107 



C. Change of dominance 112 



I). Dominance and chemistry of products of gene-action . . . 113 



/•.'. Dominance in multiple allelomorphic series 114 



/-'. The phylogenetic theory of dominance 121 



6. The gene in different doses 123 



A. Differences of dosage produced by the IX— 2X- condi- 



tions 125 



1. Sex-controlled phenotype 125 



2. Dosage through Bex-chromosomes 130 



B. Differences of dosage by deficiencies 133 



C. Differences of dosage by addition of genes 135 



vii 



4911' 



