AUTHOR S ABSTRACT OF THIS P.VPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE, MAY 1 



SPECIFIC MODIFIERS OF EOSIN EYE COLOR IN 

 DROSOPHILA MELANOGASTERi 



CALVIN B. BRIDGES 



Columbia University, New York City 



TWO DIAGRAMS 



CONTENTS 



Introduction 337 



Cream a 338 



Cream II 341 



Dark and whiting 347 



Cream III 354 



Cream b 362 



Pinkish 365 



Cream c 369 



Summary 371 



Discussion 377 



Literature cited 384 



INTRODUCTION 



The main significance of the material presented in this paper 

 is in its bearing on the question of modifying genes and the cor- 

 related question of the method by which selection attains its 

 results. A demonstration has been made of eight mutant genes 

 which by themselves produce little or no effect upon the eye 

 color of flies homozygous for them, yet which modify the eye 

 color of the sex-linked mutant 'eosin.'^ These 'specific' modifi- 

 cations are clear and simple cases of multiple genes. Each is 



^ Contribution from the Zoological Laboratory of Columbia University, and the 

 Carnegie Institution of Washington. 



^ A reference to the case of cream II and its bearing on the question of multiple 

 and modifiying genes has been made in "The Mechanism of Mendelian Heredity," 

 page 203. A brief account of the discovery and the main facts of the inheritance 

 of cream a, dark, whiting, and cream b has been given in "Non-disjunction as 

 proof of the chromosome theory of heredity," Genetics 1, page 147 ff . The impor- 

 tance in evolution of specific modifiers, typified by cream a and whiting, was 

 emphasized in "The Critique of the Theory of Evolution," pages 163 and 164. 



337 



