308 



INHERITED LINKAGE VARIATIONS 



lay. The other four cultures gave again few or no cross-overs; and 

 this type of mating was carried on for two additional generations 

 with the same result (see Appendix). It is evident that in every case 

 the tested female has at least a part of the " wild-type' ' second chromo- 

 some present in the female of culture 7 and derived from the Nova 

 Scotia stock. That this chromosome is really responsible for the 

 result has been shown in several ways, as follows: 



A wild-type female from 69 was mated to 4 black curved speck 

 males of an unrelated stock. The FI'S were wild-type and speck in 

 approximately equal numbers, as would be expected. Except for the 

 rare cross-overs, all the not-speck flies should have carried the Nova 

 Scotia chromosome; and all were heterozygous for black, curved, and 

 speck. Two such wild-type females were back-crossed to black 

 curved speck males (cultures 171 and 172). They gave similar re- 

 sults, which, when added show the following relations: 



1 2 



sp 



419 



Total 440. 



20 



Here we have the same reduction of curved speck crossing-over that 

 has already been observed for vestigial speck, which includes the 

 curved speck region, and also a reduction of the black curved cross- 

 ing-over. Experiments exactly analogous to these have been carried 

 out with curved speck, black purple vestigial arc speck, black purple 

 curved, star black purple curved speck, black purple curved morula, 

 star black plexus, and other stocks, always with the same result 

 greatly reduced crossing-over when the Nova Scotia chromosome is 

 present (see table 1). In several of these cases the chromosome in 



TABLE 1. Tests of females with one original Nova Scotia chromosome. 



question was transmitted through males, instead of females, as above, 

 but this did not in any way affect the result. 



Two wild-type females from 110 were mated to black balloon males 

 of an unrelated stock. All the offspring were, as expected, wild-type 

 in appearance. One half of them should have contained the "Nova 

 Scotia' ' chromosome, the other half should have received the vestigial 

 speck chromosome, and therefore should have given the usual result 



