162 



THE SECOND-CHROMOSOME GROUP 



distinct that when attention has been forcibly drawn to it one wonders 

 how it is possible to have been so blind. Thus, for example, the type 

 ** jaunty" having been recognized, suddenly in certain other stocks 

 wings that have been passed over as ''imperfectly unfolded" or only 

 vaguely recognized as "queer" are seen to be sharply characterized 

 " jaunties." Again, of the 20 or so mutations previously found it had 

 happened that only 2, rudimentary and truncate, bore much resem- 

 blance to each other, and we were then far less critical than now as to 

 whether a new jaunty-like mutation was actually jaunty or only a 

 mimic. To the "genus" jaunty there are now at least four well 

 recognized "species" — jaunty, jaunty X (sex-linked), curled, and Cali- 

 fornia curled. A similar mutating period for purple resulted in iso- 

 lation of maroon as a distinct but very close mimic and the "mutating 

 period of arc" brought forth arch, bow, arc2, depressed, and even other 

 types distinct in inheritance though similar in appearance ('arcoids'). 



Table 23. — Pi, jaunty 9 X black cf; Fi wild-type 99 -f- /^i wild-type cfcf . 



Table 24.— Pj, jaunty cfcf Xcurved 99; Fi wild-type 99 + Fi 



wild-type <^ cf . 



CHROMOSOME AND LOCUS OF JAUNTY. 



The fact that the gene for jaunty is carried by the "second" chro- 

 mosome appeared in the Fg from the cross of a jaunty female to a black 

 male, when a mass-culture of the Fi wild-type miales and females gave 

 a 2 : 1 : 1 : F2 ratio (table 23). The F2 jaunty flies were mated to 

 the F2 blacks, this being considered the most advantageous method of 

 working for the double recessive black jaunty. In F3 only wild-type 

 flies appeared. The blacks or jaunties, which would have indicated 

 crossing-over (in the Fi female) between black and jaunty, and which, 

 indeed, would have given black-jaunty stock in F4, did not appear. 

 Accordingly these wild-type flies, F3 offspring, which were like the 

 original Fi, were inbred to give a new F2, and many more black X jaunty 

 tests were made. Again (F5) no blacks or jaunties appeared, and this 

 indicated that the loci of black and jaunty are very close together in 

 the chromosome. On several occasions attempts were made by the 

 above method to get the double recessive. By a calculation from the 



