THE 



AMERICAN NATURALIST 



Vol. XLIX. July, 1915 No. 583 



THE ROLE OF THE ENVIRONMENT IN THE 

 REALIZATION OF A SEX-LINKED MEN- 

 DELIAN CHARACTER IN DROSOPHILA 



Professor T. H. MORGAN 

 Columbia University 

 CONTENTS 



Introduction: The Influence of the Environment. 



1. The Linkage of the Factor for Abnormal with other Sex-Linked Factors. 



(«) The Linkage of Abnormal and White. 



Gray, Red,' Abnormal by Black, White, Normal. 

 (6) The Linkage of Abnormal, Yellow, and White. 



Gray, Red, Abnormal by Yellow. White. Normal. 

 Gray, White, Abnormal by Yellow, White, Normal. 

 Yellow, White, Abnormal by Gray, Red, Normal. 

 Yellow, Red, Abnormal by Gray, White, Normal. 



2. Change of Type as the Culture Grows Older. 



3. Tests of Changed over Classes. 



4. Influence of the Factor for Black on the Realization of the Abnormal 



Character. 



5. Influence of the Factor for Yellow on the Realization of the Abnormal 



6. The Relative Influence of the Egg and of the Sperm on the Condition 



of the Heterozygote. 



7. Presence and Absence. 



8. Other Types of Abnormal Abdomen. 



9. The Non-Inheritance of an Acquired Character. 

 10. The Non-Contamination of Genes. 



INTRODUCTION 



The mutant, from which the stock with " abnormal ab- 

 domen" was derived, appeared in 1910. It is charac- 

 terized by a peculiar condition of the pigment bands and 

 segments of the abdomen as shown in Fig. 1. The range 

 of variation of the character is very great; in its most 

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