CONTENTS XI 



PAOB 



A case of partial linkage in maize 105 



Chromosome interpretation of linkage 109 



Linkage in Drosophila 110 



The factor groups 110 



An illustrative case from the first group 113 



Linkage in the second and third groups 113 



Linear arrangement of factors 115 



Application in Drosophila 116 



The mode of inheritance in crossing-over 121 



Experimental verification of theory of linear arrangement of factors 121 



Interference 122 



Linkage phenomena in other plants and animals 125 



Mathematical relations in linkage of phenomena 127 



CHAPTER VII 



THE NATURE AND EXPRESSION OF MENDELIAN FACTORS 



Introductory 129 



Conception of factors as loci in chromosomes 129 



Factors the genetic representatives of characters 129 



Manifold effects of factors 133 



The variability of factor expressions 134 



Duplicate factors . 136 



Multiple factors 137 



CHAPTER VIII 

 ALLELOMORPHIC RELATIONSHIPS IN MENDELISM 



Introductory 144 



Character relationships in Pisum 144 



Dominance defined 144 



The extent of dominance 144 



Intermediate expression in the hybrid 147 



Variable character expression in the hybrid 149 



Competitive action of factors 150 



Mosaic expression of a character 1 52 



The presence and absence hypothesis 153 



Multiple allelomorphism 155 



In Drosophila 156 



In other species 158 



Arguments in favor of the conception of multiple allelomorphism 160 



CHAPTER IX 



TYPES OF FACTOR INTERACTIONS 



Introductory 163 



Aleurone color factors in maize 163 



Comb characters in fowl. . 164 



