OF MUTANT CHARACTERS. 



247 



to cream b females of stock. There is no crossing-over in the male of 

 Drosophila, so that if cream b were in the second chromosome not 

 one of the B. C. star offspring should be cream, while half of the 

 dichaete should be cream and half not. If, on the other hand, the 

 cream were in the third chromosome, then none of the B. C. dichsetes 

 should be cream, while the star and cream should assort at random. 

 The experiment proved that the gene for cream b is in the second 

 chromosome (table 93). 



LOCUS OF CREAM b. 



An (eosin) star female and a cream b male selected from the B. C. 

 offspring gave in the next generation the amount of crossing-over 

 between star and cream b (table 94) . This value of 22.1 includes some 

 double crossing-over, and the corrected or "map" distance is probably 

 about 22.5. The chances are in favor of the cream b locus being to 

 the right of star, since star happens to occupy the leftmost of the known 

 loci. 



TABLE 94. B. C. offspring given in F 3 by an eosin star female 

 and a cream b male from table 93. 



PINKISH. 



(Plate 5, fig. 12.) 



ORIGIN OF PINKISH. 



In the fall of of 1913 a stock of eosin black had been made up with 

 which to test the chromosome group of cream II. In the following 

 summer (July 27, 1914) Bridges noticed that a few of the males were 

 somewhat lighter in eye-color than the others, but seemed chiefly 

 noticeable because of the weakness of the yellow component of the 

 eosin eye-color. The color of the regular eosin male is a pinkish 

 yellow; the color of cream a, II, III, and b is nearly a pure yellow with 

 little of the pinkish tinge, while this new color was somewhat the 

 converse of this and was a pale pink with relatively little yellow. 



One of these males mated to a sister gave all of the sons of this 

 pinkish color and all the daughters of a similar color, which is, however, 

 much harder to distinguish from standard eosin. It seems that this 

 character is somewhat sex-limited in the same direction as eosin. 



