256 



THE SECOND-CHROMOSOME GROUP 



The stock was run by mass-cultures of confluent by confluent, and 

 these also gave the same percentages of confluent. The stock was 

 maintained (with difficulty) for two years by this method and there 

 was no indication of an increase in the percentage of confluent, though 

 no counts were made. These facts prove that homozygous confluents 

 either die, as supposed, or else play only a negligible role through steril- 

 ity if they occasionally survive. 



TABLE 103. PI, confluent c? X purple curved speck 9 

 or X sepia peach ebony 9 . 



CHROMOSOME OF CONFLUENT. 



Confluent males were out-crossed to purple curved speck females (cul- 

 tures 629 and 732, table 103) and to sepia-peach-ebony females 

 (cultures 716 and 717), as PI matings for male back-cross tests to deter- 

 mine the linkage relation of confluent to the second and to the third 

 chromosomes respectively. The tests were made with great difficulty, 

 owing to the sterility and low productivity of confluent. The second- 

 chromosome tests gave a total of 71 offspring, none of which was a cross- 

 over between confluent and any of the three second-chromosome loci 

 (table 104). The third-chromosome tests gave recombination between 

 confluent and the third-chromosome loci, although as soon as the results 

 of the second-chromosome tests became apparent these third-chromo- 

 some counts were discontinued. 



TABLE 104. B. C., confluent FI d" (from taUe 103} X 

 purple curved speck 9 . 



VALUATION OF CONFLUENT. 



The very low productivity and high sterility of confluent made it 

 evident that there was little use to be obtained from the mutant in 

 spite of its dominance, good viability, and perfect separability. The 



