THE CONSEQUENCES OF CROSSING-OVER 349 



(Kulkarni, 1929 ; Bartlett, 1915 ; D., 1931 c), but the chromosome 

 constitution of the mutants has not yet been described. 



Table 55 



The Numbers of Species, Hybrids and Mutants in CEnothera having 

 Different Types of Configuration compared with their Frequency 

 if Segments were assorted at Random (after Haldane, in D., 

 1931 d). 



(iv) The Differential Segments. In order to examine these 

 assumptions, it is necessary first to consider the conditions under 

 which the chromosomes come to associate in rings during the 

 prophase of meiosis in CEnothera. Recent evidence (Catcheside, 

 1931, 1932) shows that they are the same as in other interchange 

 heterozygotes (Ch. V). Segments pair with their homologues so far 

 as they correspond ; where the correspondence ceases they change 

 partners (McCHntock in Zea, 1931 ; cf. D., 1931 d). Chiasmata 

 are formed in the paired segments, and these are terminaUsed (cf. 



