No. 576] 



VARIATION IN DROSOPHILA 



751 



to show conclusively that light and darkness do not influ- 

 ence the .percentages of Beaded-winged flies. 



IV. THE EFFECT OF SELECTION ON" THE PRODUCTION OF 

 DIFFERENT TYPES OF BEADEDNESS 



Just how much can be accomplished by selection in 

 Beaded stock was one of the first questions that arose. 

 Morgan (1911a) describes the origin of pure Beaded stock 

 as having occurred through the selection of Beaded flies in 

 the early generations after its first appearance. He says 

 the first Beaded fly found arose in a culture of Droso- 

 pliila that had been exposed to radium. Mated to his 

 sisters, 1.6 per cent, of the offspring were Beaded. When 

 these Beaded flies were inbred 3 per cent, of the offspring 

 were Beaded. These inbred gave 8.5 per cent. Beaded 

 offspring. 



The same process continued through many generations has finally 

 produced stock that gives in certain cultures nearly 100 per cent. 

 Beaded wings. 



In continuing these selection experiments, he says more 

 extreme forms of Beaded wings appeared, and at the 

 time of publishing (March, 1911) he was attempting "to 

 fix some of these extreme variations." While engaged in 

 this work other wing forms arose, most of which are 

 among the best-known mutants of Drdsophila. Among 

 these are Truncate, Miniature, Rudimentary, Vestigial 

 and Balloon wings, and the Black and Yellow body colors. 

 Most of these forms have been "purified" now and 

 Beadedness never appears in them though it can still be 

 found in Vestigial stock. All of the above-named forms, 

 by the way, with the exception of Truncate and Rudi- 

 mentary bred true from the start. The Truncate case is 

 not yet published and Rudimentary has proved (Morgan 

 and Tice, 1914) to be due to a single Mendelian factor. 

 The Rudimentary flies were at first self sterile and highly 



When I first began work with Beaded flies (Sept., 1912) 

 the stock gave 100 per cent. Beaded-winged offspring. 



