44 



SEX-LINKED INHERITANCE IN DROSOPHILA. 



point it is unlikely they will cross over again at another point nearer 

 than the average length of the loop. 



The calculation of the locus for sable gives 43.0. 



DOT. 



In the F2, from a cross of a double recessive (white vermilion) female 

 by a triple recessive (eosin vermilion pink) male, there appeared, July 

 21, 1912, three white-eyed females which had two small, symmetrically 

 placed, black, granular masses upon the thorax. These "dots" 

 appeared to be dried exudations from pores. It did not seem possible 

 that such an effect could be inherited, but as this condition had never 

 been observed before, it seemed worth while to mate the three females 

 to their brothers. In the next generation about i per cent of the males 

 were dotted. From these females and males a stock was made up 

 which in subsequent generations showed from 10 to 50 per cent of 

 dot. Selection seemed to have no effect upon the percentage of dot. 

 Although the stock never showed more than 50 per cent of dot, yet 

 it was found that the normal individuals from the stock threw about 

 the same per cent as did those that were dotted, so that the stock was 

 probably genetically pure. The number of males which showed the 

 character was always much smaller than the number of dotted females; 

 in the hatches which produced nearly 50 per cent of dot, nearly all the 

 females but very few of the males were dotted. Quite often t!he char- 

 acter showed on only one side of the thorax. 



Since this character arose in an experiment involving several eye- 

 colors an effort was made by crossing to wild and extracting to transfer 

 the dot to flies normal in all other respects. This effort succeeded only 

 partly, for a stock was obtained which differed from the wild type only 

 in that it bore dot (about 30 per cent) and in that the eyes were ver- 

 milion. Several attempts to get the dot separated from vermilion 

 failed. Since this was only part of the preliminary routine work 

 necessary to get a mutant stock in shape for exact experimentation, no 

 extfensive records were kept. 



LINKAGE OF VERMILION AND DOT. 



When a dot male with vermilion eyes was bred to a wild female the 

 offspring were wild-type males and females. These inbred gave thfe 

 data shown in table 19. 



Table 19. — Pi vermilion dot cf X wild 9 9. Fx wild-type 9 9 

 X Fi wild-type cf cT. 



