312 



INHERITED LINKAGE VARIATIONS 



treme speck end of the Nova Scotia chromosome, was mated to a 

 speck female of stock. The not-speck offspring produced were 



- , with a small piece of the Nova Scotia chromosome opposite s p 



Four females of this constitution were tested, in cultures 166, 167, 

 168, and 169, by mating to vestigial speck males. The results are 

 shown in table 7. 



TABLE 7. 



These data give approximately the usual value for vestigial speck 

 crossing-over, and therefore agree with the data previously presented 

 in indicating that there is no effect on crossing-over produced by the 

 extreme right-hand end of the Nova Scotia chromosome. 



TESTS OF CROSS-OVERS. 



When the earlier experiments with the Nova Scotia chromosome 

 were carried out, only that part of the chromosome from black to 

 speck or balloon was studied. Numerous tests of cross-overs were 

 made, in order to find out what part of the Nova Scotia chromosome 

 was responsible for the unusual ratios. The result obtained was that 

 that part of it that lies to the left of a point between purple and vestigial 

 gave approximately the ratios found in ordinary stocks; but that 

 part of it that lies to the right of this point between purple and vestigial 

 and to the left of a point between curved and speck gave what seemed 

 at first to be the same ratios as those given by the whole Nova Scotia 

 chromosome. It was therefore concluded that the peculiarity was 

 due to one gene, located between purple and speck. But it soon 

 appeared that this right-hand end was giving a little more crossing- 

 over in the black-curved region than was the whole Nova Scotia 

 chromosome. By this time star had become available, and it was 

 now found that star and black gave no cross-overs in the presence of 

 the whole chromosome, but gave the usual 40 per cent in the presence 

 of the right-hand end. Tests were then made of the left-hand end 

 again, and star and black were found to give no cross-overs, while 



