292 



THE SECOND-CHROMOSOME GROUP 



present. A mass-culture of the telescope females and telescope males 

 which showed none of the sex-Unked character was made (2867). 

 This culture failed, probably because of sterility rather than from cul- 

 tural conditions, since some of these same flies remated to purple, in or- 

 der to start a second-chromosome linkage test with telescope failed to 

 produce offspring (3120, 3121, 3122). A second mass-culture of 

 telescope (2906) produced a very few flies, from which a successful out- 

 cross of a telescope female to a male from the pink spineless stock 

 (third-chromosome recessive) was made (3213; 3214 sterile). Several 

 Fi pairs were started, of which one (3503) produced offspring. These 

 offspring represented a 9 : 3 : 3 : 1 ratio of telescope and pink (+ 188, 

 ts 61, p 44, tsP 12; disregarding spineless), which proved that telescope 

 was not in the third chromosome. 



This culture furnished (March 4, 1916) one of the most valuable 

 autosomal characters, hairless, a third-chromosome dominant which is 

 fully viable (though lethal when homozygous), which is easy of clas- 

 sification, which does not mask any other third-chromosome character, 

 and whose locus is advantageous. 



After the discovery that telescope was not in the third chromosome 

 it was thought certain that it was in the second, so experiments 

 were planned on that basis. By means of the dominant "star," at 

 least a rough approximation of the locus was possible. Accordingly 

 several out-crosses to star were made en masse (3848, 3849, 3854), 

 of which 3854 alone produced offspring. In view of the sterility so 

 far encountered it was thought best not to attempt back-crosses, but 

 to raise F2 which involves the mating only of not-telescope flies. The 

 first tests were to check up the assumption that telescope was second- 

 chromosome by means of a male test. This was done by pairing the 



Fi star males ( j and Fi wild-t3TDe females f — J. The telescope 



offspring, then, constitute a back-cross test. The result proved, as 

 expected, that the telescope is second-chromosome, for none of the 

 back-cross telescopes were star (table 136). 



Table 136. — Pi, telescope 9 9 Xstar cfcf; Fi star d^ 4- ^i wild-ttjpe9. 



At this time the mass stocks of telescope were producing better 

 (4313, 4516, 4636), so some female back-cross tests were attempted. 

 Of the first lot one (4400) succeeded fairly well, but no counts were 



