OF MUTANT CHARACTERS. 



203 



STOCK OF ARC. 



The character arc had appeared in females as well as males, so 

 that material was on hand to establish 'a stock. A mass-culture 

 produced a stock that seemed to be pure. Several pair matings made 

 at the same time proved completely fertile, and from one of these a 

 permanent stock was started. 



INHERITANCE OF ARC. 



In crosses of arc to wild all the FI flies were wild-type, showing that 

 arc is recessive. Three mass-cultures and two pairs of FI flies gave a 

 total of 2,596 offspring, of which 648 or 24.8 per cent were arcs (table 48). 



TABLE 48. PI, arc 9 9 X mid d" dV FI wild-type 9 9 X FI wild-type d* a". 



EPIDEMIC OF ARCS. 



Just as in the cases of purple and of jaunty, there was a short period 

 following the discovery of arc during which arcs appeared and in the 

 most diverse stocks. Within 6 months 9 other appearances of arcs 

 had been recorded by Bridges (table 47). Of these, arc 8 proved to 

 be sex-linked (bow), and at least 2 others were not arc itself, since 

 when bred to arc they gave straight wings. Arcs 7 and 9 were the 

 same as (or at least allelomorphic to) the original arc. Both of these 

 occurred in distinct stocks and were probably independent appear- 

 ances. Cultures B 66 and B 67 (table 48) are F 2 's from arc 7 by wild. 



CHROMOSOME CARRYING ARC. 



At this time (June 1912) the autosome groups were still very nebu- 

 lous. The " second" group was slowly condensing around black, but 

 so far as recognized comprised only black, curved, purple, and vestigial, 

 though other mutants had been found which later evidence showed 

 were second chromosome. The key tests had not yet been made 

 which linked all of these into a solid system. The third chromosome 

 group was in far worse plight, being defined simply by pink. It was 

 for this reason that in testing the chromosome of arc some experiments 

 were made that would now be useless. For example, arc was crossed 

 to pink and gave in F 2 a close approach to a 9 :3 :3 : 1 ratio (table 49). 



