GENETICS PURPLE EYE COLOR DROSOPHILA 



279 



REPETITION OF THE PURPLE VESTIGIAL BACK-CROSS TESTS 



Because of the number of disturbing conditions that had been 

 met with in the first set of tests of the linkage of purple and 

 vestigial, a second and more extensive set was started. These 

 second experiments were carefully planned, and in the results ob- 

 tained approach present standards of uniformity and rehability. 

 The viabiUty of vestigial was excellent, and the equahty of con- 

 trary classes throughout the experiments speaks for the favorable 

 culture conditions. The new experiments were conducted with 

 a purple vestigial stock descended from that used in the experi- 

 ments of table 3, but cleared of mutations and perhaps other 

 disturbing factors by outcrossing to wild and by selection started 

 among the F2 progeny and maintained for several generations 

 until it seemed probable that the stock was clean. Also, from 

 the progeny of table 3 some purple Tnot-vestigialj crossovers 

 were selected, and from them was secured in a few generations 

 a simple purple stock free from vestigial and from the other 

 mutant characters known to be present. A preliminary test of 

 the qualities of this purple stock was made by outcrossing a male 

 to a wild female and carefully examining all F2 flies Stable 4j. 

 The F2 showed only purple (loOj and wild-type (300 J flies as 

 expected, but the ratio was 1:2 instead of 1:3. ^^^lile this 

 deviation was significant (4.1 times the probable error), it 

 indicated a peculiarity of the wild parent rather than of the 

 purple, and was not further regarded. The vestigial stock used 

 was that from which purple itself was derived. It had been 

 examined frequently and seemed to be clean. 



TABLE 4 

 The Fi offspring from the cross of a purple male to a wild female 



