SEX-LINKED FACTORS IN DROSOPHILA 45 



SCOPE OF THIS INVESTIGATION 



It would seem, if this hypothesis be correct, that the proportion 

 of 'cross-overs' could be used as an index of the distance between 

 any two factors. Then by determining the distances (in the 

 above sense) between A and B and between B and C, one should 

 be able to predict AC. For, if proportion of cross-overs really 

 represents distance, AC must be approximately, either AB plus 

 BC, or AB minus BC, and not any intermediate value. From 

 purely mathematical considerations, however, the sum and the 

 difference of the proportion of cross-overs between A and B and 

 those between B and C are only Iwiiting values for the proportion 

 of cross-overs between A and C. By using several pairs of 

 factors one should be able to apply this test in several cases. 

 Furthermore, experiments involving three or more sex-linked 

 allelomorphic pairs together should furnish another and perhaps 

 more crucial test of the view. The present paper is a prelim- 

 inary report of the investigation of these matters. 



I wish to thank Dr. Morgan for his kindness in furnishing 

 me with material for this investigation, and for his encouragement 

 and the suggestions he has offered during the progress of the 

 work. I have also been greatly helped by numerous discussions 

 of the theoretical side of the matter with Messrs. H. J. Muller, 

 E. Altenburg, C. B. Bridges, and others. Mr. Muller's sugges- 

 tions have been especially helpful during the actual preparation 

 of the paper. 



THE SIX FACTORS CONCERNED 



In this paper I shall treat of six sex-linked factors and their 

 inter-relationships. These factors I shall discuss in the order in 

 which they seem to be arranged. 



B stands for the black factor. Flies recessive with respect 

 to it (b) have yellow body color. The factor was first described 

 and its inheritance given by Morgan ('11 a). 



C is a factor which allows color to appear in the eyes. The 

 white eyed fly (first described by Morgan '10) is now known to 

 be always recessive with respect both to C and to the next factor. 



