IN THE SECOND CHROMOSOME. 



309 



Table 2. 



for black balloon (48 per cent). 12 of these females were back-crossed 

 to black balloon males, and gave the two types of results shown in 

 table 2. 



The experiments described above 

 demonstrated that the unusual result 

 is produced when the Nova Scotia 

 chromosome is present; the black bal- 

 loon result and other similar ones show- 

 that offspring of individuals bearing 

 such a chromosome may give the usual 

 result, these evidently being the off- 

 spring that do not receive the chromo- 

 some in question. Table 1 shows the 

 results obtained from females bearing 

 one Nova Scotia chromosome. 



Since there is here a total of only 

 about 1.5 per cent crossing-over 

 between star and speck, it follows that we have almost certainly \)een 

 dealing throughout with a second chromosome derived entirely (or 

 at least all of it between star and speck) from the original Nova Scotia 

 stock. 



In culture 193 a female heterozygous for curved and speck and for 

 the Nova Scotia chromosome was mated to a curved sixick male. 

 A speck female, produced as the result of crossing-over between curved 



Table 3. — Tests of females with one Nova Scotia chromosome, 

 the speck end of which has been replaced. 



and speck (and therefore bearing the original Nova Scotia chromo- 

 some, minus its speck end) , was mated to a curved male of stock. Two 

 daughters of the latter culture (in 283 and 284) gave 1 cross-over be- 

 tween curved and speck in 505 offspring. The results obtained with 

 this Nova Scotia chromosome, from which the speck end liivd been 

 removed, are shown in table 3. Evidently the speck end of the chromo- 

 some is not responsible for the unusual results. 



As will be shown below, the Nova Scotia chromosome was ultimi\t4>ly 



i separated into two parts, the separation-point being betwwn purple 

 and vestigial. Tests (see table 16) were made of fenuiles in which 

 both parts were present, but were each united to parts of "normal" 



'chromosomes. Culture 778 w^as of this nature; and 786 and 787 

 contained daughters of 778 in which the original Nova Scotiii chromo- 



