CONDITIONS OF AMEIOSIS 



401 



of derivatives of this hybrid to F. anindinacea (6x = 42) some 

 seedhngs had seven bivalents and fourteen univalents, while others 

 had complete pairing. 



Finally, there are organisms in which the later stages of meiosis 

 are abnormal, although the earlier stages showed no defect in 

 pairing. 



The evidence of genotypic control may thus be direct or it may 



Table 60 



The Causal Relationships of Different Kinds of Non-pairing of 

 Chromosomes at Meiosis. 



merely exclude the possibility of structural control. The exclusion 

 of environmental control is not important for an analysis of the 

 mechanism, since in effect it is analogous and in function it is 

 complementary to genotypic control. Thus in Allium odonim 

 (Modilewski, 1930), which is true-breeding, embryo-sac mother- 



