LINKAGE RELATIONS IN MEN DELI SM 



119 



of chromatin have occurred which affect the relations of the factors to 

 each other, so that this type of separation after synapsis gives the non- 

 cross-over gametes (wmB'X) and (WMb'X). Types B and C involve 

 single breaks in the chromosomes followed by chromatin interchange in 

 reunion. They are the single cross-overs and give the cross-over gametes 



B' 



,K A 



m 



B' B' 



46.3 28.15 15.45 10.1 



FIG. 55. Diagram to show crossing-over in a three-factor experiment. 



(wMb'X) and (WmB'X) and (wmb'X) and (WMB'X) respectively. 

 Finally in type D the chromosomes have broken and exchanged material 

 at two points. This type is called double crossing-over and results in 

 the production of gametes of the genetic constitutions (wMB'X) and 

 (Wmb'X). In this last case, although chromatin interchange has 

 occurred between the two chromosomes, the relations between the loci 

 W and B' remain unchanged. 



