MUTATIONS IN EYE-COLOR OF DROSOPHILA. 335 



The Fi Back-Crosses— The two following schemes give the P, generation: 

 P x 9 by P <? P, p 9 by # 



p, p 9 o * f x Ti — p-^ 



When P 9 (from 9 by P c?) is back-crossed to P <? the expectation is 2 pink 

 9, 1 pink cf, 1 orange <?. The results gave: 



Pi Pink 9 31 Pink d" 18 Orange <j 15 



When P 9 (from P 9 by <?) is back-crossed to d" the expectation is for 

 equality in all four classes. The results gave: 



Pi Pink 9 106 Pink tf 76 Orange 9 120 Orange <? 100 



Further Tests of Pi — In several cases the Pi's were tested with the other color 

 from pure stock. Thus: When P 9 (from 9 by P d" ) is mated with pure 

 <? the expectation is for equality in all four classes. The actual results were: 



110 T109 f 91 f 100 



Pink 9 \ 102 Pink <*» \ 70 Orange 9 \ 90 Orange <*» \ 73 



44 I 41 I 45 I 44 



256 220 226 217 



When P cT (from P 9 by O d") is tested with pure O 9 the expectation if 

 pink 9 and orange 6* in equal numbers : The results were : 



Pink 9 | 109 Orange <f I 



278 



107 



393 385 



When P 9 (from P 9 by O <?) is tested with P <*■ the expectation is 2 

 pink 9 , 1 pink d" , 1 orange d" : The results were : 



Pink 9 46 Pink c^ 20 Orange cf 19 



Counter-Crosses. — The P^s from O 9 by P d" were mated to the Pi's from 

 P 9 by O cf. Such crosses I shall call counter-crosses. 



When P 9 (from P 9 by O d) is mated to the O & (from 9 by P <?) the 

 expectation is for equality in four classes. The results were : 



Pink 9 jJ Phkd-j" Orange 9 {^ Orange , {J 



110 162 195 166 



When P 9 (from O 9 by P d») is mated toOcf (from P 9 by cf ) the 

 expectation is 2 pink 9 , 1 pink cf, 1 orange d* . The results were: 



Pink 9 157 Pink <*■ 22 Orange cP 73 



