A MUTATION IN THE MOTH-LIKE FLY. 133 



all spe< -mien- were brown-eyed. The remaining lots contained 

 both brown-eyed and white-eyed progeny, the white-eyed 

 varying in pr< .portion from 27 to 58 per cent, of the total number 

 in each lot . 



(1. Discussion of Res nils in Preliminary 



I re-ults of the preliminary crosses indicated that the 



norni.il .mdition was behaving as a dominant and the mutation 



pun- ive. Assuming that the normal condition i BB) 



was dominant and the mutant condition (b : ive -i\ 



ibl( :- ses could be made and the expectations in the 



progeny would lie as follows: 



Expected Ratios I'li.-n. 



< bb. . . . . . 100 % white-eyed 



BB X BB . 100 % brown-eyed 



BB X Bb .100 % brown-eyed 



X Bb. 15 c /i brown-eyed. . ; 



BB X ' .100 % brown-eyed 



Bb X > . . 50 % brown-eyed, 50 r [ \vliiu--< yed 



The I'u 11 expectation was realized in the preliminary bb by bb 

 crosses. 



Since both pure brown-eyed (BB) and h\brid- / v 

 contained in the mass cultures from which the breeding -ii.ck \\a- 

 -elected it would be expected that the brown-eyed by bn>\\ n-e\ed 

 < i "-ses might be either BB by BB or BB by Bb in which case .ill 

 of the ln>t filial generation would be brown-eyed: or tin \ \\..nld 

 be H''i 1>\ lib in which case there would be expected a 1 

 pn.pi .nit m of brown-eyed individuals and a te\v white-eyed one- 

 in the tir-t filial generation. This expectation \\.i.- al-o appn>\i- 

 m.iteU reali/ed in the preliminary brown-eyed \>y l.ro\\n-e\i<l 

 in that a small proportion of white-eyed -perimen- were 

 procured fn.m such crosses. 



In the brown-eyed by white-eyed crosses there \\eix t\\< 

 -ibilities, namely, that the brown-eyed specimen- u-ed were 

 either pure (BB) or hybrids (Bb). If the brown-eyed parents 

 \\eie pure all the progeny of the first filial generation would be 

 bn>\\ n-cycd. It" the brown-eyed parent- \\ere hybrids then 50 

 per cent, "t the first filial generation would be white-eyed. 

 This expectation was realized in some lots as far as the securing of 



