GENETICS PUKPLE EYE COLOR DROSOPHILA 293 



locus experiment just given provided more accurate measures of 

 the map distances involved. The preparation of the multiple 

 recessive and of the Pi stocks delayed the completion of the 

 experiment for nearly a year (January, '14). Meanwhile, these 

 provisional locations were used as the basis for locating certain 

 other genes more closely. The first of these was curved. 

 Bridges and Sturtevant (Biol. Bull., '14) soon found (January, 

 '13) that black and curved gave approximately 23 per cent of 

 crossing over. The next point to be determined was the relation 

 of curved and one of the other two mutations whose loci had been 

 mapped. Both of these tests were used, since each offered 

 advantages; the chief disadvantage was that vestigial interferes 

 with the classification of curved, so that it is impossible to dis- 

 tinguish between the simple vestigial and the vestigial curved 

 class. 



The purple curved test was undertaken by Bridges, who 

 prepared to run a three-point back cross involving black purple 

 and curved. The first step was the synthesis of the purple 

 curved double recessive. As soon as this was obtained it was 

 turned over to W. S. Adkins, who ran a preliminary back-cross 

 test of the simple purple curved crossing over, and found that 

 there was about 18 per cent of crossing over. This enabled us 

 to determine the relation of curved to the other three genes. 

 The purple curved value of 18 showed that curved was closer to 

 purple than to black (black curved = 23) and that purple and 

 vestigial were therefore 'to the right' of black. Curved was 

 further to the right than vestigial since black and vestigial gave 

 only about 18 per cent of crossing over. 



The vestigial curved distance was tested by Sturtevant, who 

 found that there was about 8.5 per cent of crossing over. Be- 

 cause of the difficulty of classification already referred to, it was 

 not thought worth while to run these tests on a large scale. 

 However, vestigial is itself accurately mapped and is nearer to 

 curved than purple is. These considerations are strong enough 

 to warrant an extension of the vestigial curved tests which may 

 furnish the main basis for the accurate mapping of curved. 



