INVERSION PAIRING 



i8i 



is often repeated ; there has been a duplication of translocated 

 segments in the history of the species. 



The relationship of the enlarged chromosomes with those found 

 in ordinary mitotic and meiotic nuclei has been traced by Roller 

 (1935). As the nucleus grows the chromosome threads become 



*-Tnv. 



Fig. 63. — Complete nucleus in the O hybrid, D. pseudo-obscura, 



Race A X Race B, showing the presence of five inversions and 



one possible deletion, x 750 (Roller, 1935). In opposite corners 



the mitotic chromosomes of these two races {S) are shown. 



X 3000 (D., 1934). 



thicker and it is presumably during this stage that they multiply 

 by division. They show the relic coils characteristic of a mitotic 

 prophase and consistent for given arms of a chromosome. In this 

 condition they pair. They then show (but much more clearly on 

 account of their great size) the relational coiling seen between 

 meiotic partners at pachytene. The torsion that produces this 



