MORGAN 



All of the offspring should be white, 

 and male and female in equal numbers; 

 this in fact is the case. 



Second Verification. — As stated, 

 there should be two classes of females 

 in the Fo generation, namely, RRXX 

 and RWXX. This can be tested bv 

 pairing individual females with white 

 males. In the one instance (RRXX) all 

 the offspring should be red— 



RX-RX (female) 



WX-W(male) 



RWXX - RWX 



and in the other instance (RWXX) 

 there should be four classes of individ- 

 uals in equal numbers, thus: 



RX-WX (female) 



WX-W(male) 



RWXX— WWXX - RWX— WWX 



Tests of the Fo red females show^ in 

 fact that these two classes exist. 



Third Verification.— T\\t red Fi fe- 

 males should all be RWXX, and should 

 give with any white male the four 

 combinations last described. Such in 

 fact is found to be the case. 



Fojirth Verification.— The red Fi 

 males (RWX) should also be hetero- 

 zygous. Crossed with white females 

 (WWXX) all the female offspring 

 should be red-eyed, and all the male 

 offspring white-eyed, thus: 



RX-W (red male) 

 WX - WX (white female) 

 RWXX - WWX 



Here again the anticipation was 

 verified, for all of the females w'ere 

 red-eyed and all of the males were 

 white-eyed. 



CROSSING THE NEW TYPE WITH 

 WILD MALES AND FEMALES 



A most surprising fact appeared 

 when a white-eyed female was paired 



65 



to a wild, red-eyed male, /. e., to an 

 individual of an unrelated stock. The 

 anticipation was that wild males and 

 females alike carry the factor for red 

 eyes, but the experiments showed that 

 all wild males are heterozyCTous for red 

 eyes, and that all the wild females are 

 homozygous. Thus when the white- 

 eyed female is crossed with a wild red- 

 eyed male, all of the female offspring 

 are red-eyed, and all of the male off- 

 spring white-eyed. The results can be 

 accounted for on the assumption that 

 the wild male is RWX. Thus: 



RX-W (red male) 



WX - WX (white female) 



RWXX (50%) -WWX (50%) 



The converse cross between a 

 white-eyed male RWX and a wild, 

 red-eyed female shows that the wild 

 female is homozygous both for X and 

 for red eyes. Thus: 



WX-W (white male) 



RX-RX (red female) 



RWXX ( 50% ) - RWX ( 50% ) 



The results give, in fact, only red 

 males and females in equal numbers. 



GENERAL CONCLUSIONS 



The most important consideration 

 from these results is that in every point 

 they furnish the converse evidence 

 from that given by Abraxas as worked 

 out by Punnett and Raynor. The two 

 cases supplement each other in every 

 way, and it is significant to note in this 

 connection that in nature only females 

 of the sport Abraxas lacticolor occur, 

 while in Drosophila I have obtained 

 only the male sport. Significant, too, 

 is the fact that analysis of the result 

 show^s that the wild female Abraxas 

 grossulariata is heterozygous for color 

 and sex, while in Drosophila it is the 

 male that is heterozygous for these 

 two characters. 



