160 THE SECOND-CHROMOSOME GROUP 



female (from II 144, table 20) was outcrossed to a speck male, with the 

 regular result shown in table 22. Two of the FI free-veined females 

 were back-crossed to speck males (table 22). There were 36 free- 

 veined flies, of which only 3 or 8.3 per cent were speck, i. e., cross-overs. 

 Since black gives about 48 per cent of apparent crossing-over with 

 speck and only 41.5 with free- vein, it is probable that the gene for 

 free-vein lies to the left of speck rather than to the right. Certain 

 more recent work makes it probable that the locus of blistered is con- 

 siderably nearer to speck, perhaps only two units away, or at 103 =*= . 



JAUNTY 0). 



(Plate 7, figure 3.) 



DISCOVERY AND STOCK OF JAUNTY. 



Shortly after the discovery of " blistered," the wing mutation 

 "jaunty" was found by Bridges (December 11, 1911) in the same 

 stock, rudimentary, in which blistered had appeared. On account of 

 the low productivity of rudimentary females, the rudimentary stock 

 was being carried on by continually back-crossing rudimentary males 

 to heterozygous females. When this method is used, only half of the 

 flies in each generation are expected to show the character rudimentary, 

 the other half being wild-type. The first jaunty seen was one of the 

 not-rudimentary females (notebook A, p. 34) whose wings turned up 

 "jauntily " at their tips. Next day a jaunty male appeared in the same 

 culture. The fact that the character had appeared in both sexes 

 suggested that it was not sex-linked unless dominant. These two 

 jaunties were bred to wild-type flies of the same culture and in FI gave 

 offspring none of which showed a trace of jauntiness. That is, jaunty 

 was recessive and autosomal (not sex-linked). Jaunty reappeared in 

 F 2 as approximately a quarter of the flies of both sexes, but no accu- 

 rate counts were made because the presence of another wing-charac- 

 ter, rudimentary, tended to make the classification difficult. To mate 

 mutants to flies of the stock in which they first appear is poor policy 

 because of this presence in succeeding generations of characters which 

 are more apt to be hindrances than helps. In this case it required 

 continued selection of the jaunty not-rudimentary individuals to 

 establish a stock that was pure for jaunty and entirely free from 

 rudimentary. 



DESCRIPTION OF JAUNTY. 



The wings of jaunty flies are turned upward at their tips, the curva- 

 ture usually involving only the terminal third or half of the wing, 

 though sometimes the basal region is also more or less curved. The 

 amount of curvature is rarely great enough so that the tip is at right 

 angles to its normal position, the usual curvature being through 30 to 



