324 



INTRODUCTION TO CYTOLOGY 



over is of about equal frequency in all regions; hence the genes in the 

 middle region were assigned to loci too close together. In a similar 

 manner it has been shown that several genes shown very near the "right" 

 end of chromosome I in the genetic map must lie much farther to the 



y scslvh brpnwecrbcvolxcf t V m g rfBBxfucrnbb 



CEX 



a! dp d b prBltkcn c 



jOO 110 



px sp 



ru 



D th 



IP 



a 



»J-^ 



D th St p 



coi HI 



cu 



sr 



ca 



Fig. 185. — Comparison of " genetical maps" of chromosomes I, II, and III of Drosophila 

 melanogaster with "cytological maps" of these chromosomes in metaphase as indicated by 

 translocation data, sp, spindle-attachment region. Cf. Fig. 173. {After Dohzhansky, 

 1932a, 1930d, 1929a.) 



"left," the right end with the spindle-attachment point being for the 

 most part devoid of known mutant genes. ^^ The older genetic maps still 

 serve as diagrams of the order of the genes and their crossover values, 

 but they may not show accurately the true spacing. It is to be remem- 



" For chromosomes II and III, see especially Muller and Painter (1929) and 

 Dobzhansky (1929aft, 1930ad, 19316). For chromosome I (X-chromosome), see 

 Painter (1931) and Dobzhansky (1932a). 



