OF MUTANT CHARACTERS. 



241 



STOCK OF CREAM II. 



From the F 2 a few cream males were selected and bred to their 

 sisters, all of which were wild-type in appearance, though a quarter 

 of them were homozygous for the cream gene (not-eosin creams). 

 This mass-culture gave the expected cream females and males, from 

 which a pure-breeding stock was made up. There was a difference 

 in the color of the males and females of this pure stock, the difference 

 being of the same order as the normal bicolorism of eosin. 



A complete separation of the eosin from the eosin heterozygous for 

 cream had not been attempted in the original F 2 culture. In order to 

 observe the heterozygous condition more closely a cream male from 

 the pure stock was out-crossed to an eosin female. The FI flies both 

 males and females (culture M 68, intermediate males 73, intermediate 

 females 88) 1 were lighter in eye-color than standard eosin, though the 

 difference between eosin and these heterozygotes was less than the 

 difference between the heterozygotes and the pure cream. 



TABLE 89. Fz offspring from the cross of a cream male to an eosin female. 



Among these F 2 offspring (table 89) there were six different eye- 

 colors; among the males, the same three that occurred in the original 

 F 2 , and among the females three colors which, though corresponding 

 genetically to the classes among the males, were darker in eye-color. 

 The cream female is lighter than the eosin male, while the heterozy- 

 gous cream female is somewhat darker than the eosin male. In order 

 from the darkest (a deep slightly yellowish pink) to the lightest (a 

 pale translucent yellow) the six colors are: eosin female, heterozygous 

 cream female, eosin male, heterozygous cream male, cream female, 

 cream male. The females were first separated from the males. Then 



1 One of the 88 intermediate daughters had only three segments to her abdomen instead of the 

 usual five. This female (figured by Morgan, 1915, p. 425, text-figure 3a) was the founder of a 

 new type of abnormal segmentation of the abdomen "patched." The segments were reduced 

 in number (as in the first specimen), or, more typically, were cut sharply into oblique or triangular 

 pieces which were patched together as illustrated in figures 6 to/, of plate 11. This character 

 was recessive, but it generally reappeared in very much less than a quarter of the F 2 offspring. 

 The usual causes for such deficiencies are poor viability, partial or complete dependence for 

 realization on the coaction of one or more other genes, or failure to be developed in all the flies 

 fluctuations of pure for the gene, whether from environmental differences or because the normal 

 genetically the character overlap the wild-type. The gene for patched was in the second chro- 

 mosome, as shown by its strong linkage to the cream. 



