152 



STRUCTURAL HYBRIDS 



is fairly evident. An association with interstitial chiasmata is 

 relatively rigid ; its shape shows little variation, and is determined 

 by the number and distribution of the chiasmata. It is a three- 

 dimensional system. An association with terminal chiasmata is 



Nor ma/ 

 rromo^i/^'al-e 



^^^^^ 

 b a 



/ncerswn 

 ne/frojy^ffi'e 



Deficienci/ 



C D 



A/orma/ Nomo^ygole 



••WWW^ 



In/erc/ian^e //e/'ero^i/^'o/e 



D/sJitrjdion 





Fig. 52. — Above, structural relations of homozygotes and hetero- 

 zygotes for different changes. Below, chain and ring formation 

 with different numbers of chiasmata showing different kinds of 

 disjunction. 



extremely pliable ; the variation found in its shape shows that (as 

 might be expected) any two chromosomes move freely in relation 

 to one another unless they are associated at hoth ends. It is a two- 

 dimensional system. Forces of repulsion associated with the 

 centromeres are therefore able to effect regular disjunction of a 



