OF MUTANT CHARACTERS. 135 



OLIVE. 



ORIGIN AND STOCK OF OLIVE. 



The origin and early history of the stock called "olive," because of the 

 body-color present, is only partly a matter of record, though the account 

 given in the section on speck is substantially correct. To repeat: In 

 the fall of 1909, Morgan started selection on stocks of wild flies that 

 were throwing individuals with extra-dark trident patterns. One line 

 of selection eliminated this variation, and the resulting "without" stock 

 represented the original wild stock before the occurrence of the "with" 

 mutation. It was in this "without" stock that the old speck was 

 found. The selection in the opposite direction isolated the third- 

 chromosome semi-dominant mutation "with" (plate 5, fig. 3). The 

 "olive" stock appears to have resulted from selection carried out on a 

 stock different from that which gave rise to "with." The trident pat- 

 tern of the "olive" stock is dark, but is not distinct, being submerged 

 in a general olive color that suffuses the thorax. The "olive" stock 

 was obtained about May 1910, and had been kept in the stock room 

 about a year when it was noticed that it was pure for speck. 



CHROMOSOME AND LOCUS OF OLIVE. 



During the fall and winter of 1912 several crosses were carried out 

 by Miss Wallace with the " olive " stock. " Olive " crossed to wild gave 

 wild-type offspring which were inbred in pairs to give F 2 . This cross 

 and the reciprocal were both made and gave the same kind of FI and F 2 

 results in the distribution of both characters and sex, showing that no 

 important sex-linked modifiers of body-color were present. The com- 

 bined F 2 counts (2,857 flies) gave a very perfect 9 : 7 ratio of gray to 

 "olive" (1,622 : 1,235), showing that the "olive" stock contained two 

 recessive dark body-colors whose genes assorted independently (tables 2 

 and 3) . A further separation of the " olive " classes into the component 

 two single and the double recessive forms was not attempted. That 

 one of the recessives (olive II) was carried in the second chromosome 

 was proved by the strong linkage olive showed with speck (tables 2 and 

 3). There were only 2.3 per cent of flies that were speck not-olive. 

 The whole observed distribution corresponds to about 14.3 per cent of 

 crossing-over between speck and olive. It is certain that this value is 

 far too high due to the difficulty in classifying the olive. Our later 

 experience has been that olive is probably less than a unit distance from 

 speck, and probably to the right, which give an approximate locus of 

 106 when referred to star. 



Very rarely have we secured speck flies that we consider free from 

 olive. The original stock of speck was probably not-olive, and in a 

 certain experiment made by Sturtevant (1915) it seems likely that the 



