9 6 



Scientific Proceedings (98). 



relation between the sex ratio of a culture and the pedigree of the 

 parents — in fact, two cultures from the same parents may give 

 quite different sex ratios. 



Preliminary experiments indicate that environmental con- 

 ditions — especially temperature — affect the sex ratio in this line; 

 but we are not yet able to control it at will. 



In this race the females frequently have abnormal abdominal 

 bands; but this character appears in the males only very rarely. 

 The evidence indicates that it is this character that is influenced 

 by environmental conditions, and that the very abnormal females 

 do not emerge from their puparia. Dark pupa?, evidently dead, 

 are always to be found in cultures that give a significant excess of 

 males. A few of these have been dissected, and have been found 

 to contain dead flies with abnormal abdomens. In the few cases 

 in which the sex was determined, these were females. 



When the race here described is crossed to unrelated races, the 

 sex ratio in Fi approximates 1:1, and the F x females do not have 

 abnormal abdomens. Both characters, however, reappear in the 

 next generation. These crosses show also that the characters are 

 both transmitted by males as well as by females. 



These data indicate that abnormal abdomen is a recessive 

 sex-limited mutation. It commonly affects only females, and 

 the degree of the abnormality produced is dependent on environ- 

 mental conditions. When the abnormality is extreme the females 

 do not emerge, and an excess of males results. 



56 (1431) 



The construction of chromosome maps. 



By T. H. Morgan and C. B. Bridges. 



[From the Zoological Laboratory, Columbia University, New York 



City.] 



The accuracy with which a chromosome map may be con- 

 structed depends upon several conditions. (1) The mutant char- 

 acters employed should be carefully restricted to those cleanly 

 separable both from the wild type and from each other, and whose 

 viability is practically the same as that of the wild type. (2) 



