SHORTER ARTICLES AND DISCUSSION 



VIABILITY AND COUPLING IN DROSOPHILA 



In the course of Avork done in the college year, 1911-12, under 

 the direction of Dr. Castle, at the Harvard Zoological Laboratory, 

 ( 'ninlirirlii'o, .Mass.. an experiment was performed to test the rela- 

 tive viability of the red-eyed and the white-eyed stock of Droso- 

 phila ampelopkila Loew. The white-eyed race was obtained from 

 Professor Morgan, while the red-eyed material was reared from 

 banana exposed near the laboratory. 



A large glass jar well supplied with fermenting banana and 

 tightly covered with a double layer of closely woven cheese-cloth 

 was used for the experiment. Five pairs of flies from the red- 

 eyed stock and five pairs from the white-eyed stock were intro- 

 duced on November 29, 1911. After a few weeks the jar was 

 well supplied with flies of both eye-colors, but the red-eyes con- 

 siderably surpassed the whites in number. Fresh food was in- 

 troduced once and on February 12 a number of the flies were 

 drawn off and counted. 



Let us consider here what the expectation of the ratio between 

 reds and whites would be, after the culture had been running 

 indefinitely. Assuming equal viability of the two races, we should 

 expect equality of reds and whites among the males, and three 

 reds to one white among the females. This appears from the 

 following combinations based upon Morgan's formulae. The mu- 

 tation producing white eyes, being recessive to the wild type, has 

 been denoted by a small letter as suggested by Castle. 1 



Red female gives gametes x and x. 



White female gives gametes wx and wx. 



Red male gives gametes x and — . 



White male gives gametes wx and — . 



The combinations will then be as follows : 

 2wx — = 2 white males, 1 x x ^ 

 2x — = 2 red males, 2 wx x J 

 1 wx wx 



lli Simplification of Mendelian Formula;," 

 XLVII, 555, March, 1913. 



= 3 red females, 

 = 1 white female. 

 American Naturalist, 



