on the validity of torsion coiling and the relational coiling of homologues, 

 both of which are somewhat doubtful. Furthermore, analysis of types of 

 pairs of chiasmata (Huskins and Newcombe, 1941) in Trillium and the 

 grasshopper fail to fit spatial expectations without involving complex and 

 unlikely modifications. 



Figure 6-9, Schematic Representation of Chiasmata Formation: (a) rela- 

 tionship of homologous chromosomes prior to chiasmata formation; (b) 

 formation of chiasmata by breakage and rejoining of chromatids; (c) clas- 

 sical mechanism of chiasmata formation as proposed by Sax (1932). 



Duplication Theory 



Duplication of chromosomes followed by longitudinal joining of the 

 chromomeres, which, if overlapping of homologues occurs, may result 

 in the joining of chromosomes from homologues rather than from the 



MECHANICS AND PHYSIOLOGY OF CELL DIVISION / 153 



