LINKAGE 



385 



there are those who deny any fusion at all between the members of the 

 pair, holding rather that their identity is not impaired in any way during 



FIG. 149. The behavior of the conjugating homologous chromosomes according to 

 the Chiasmatype Theory of Janssens. Single crossing over at left; double crossing over 

 at right. (Adapted from Babcock and Clausen.) 



FIG. 150. Crossing over between 2 of the 4 chromatids of the chromosome tetrad, giving 

 2 crossover and 2 non-crossover gametes. (Adapted from Janssens, 1909.) 



FIG. 151. Chromosomes of Batracoseps attenuatus, showing chiasmas. (After Janssens.) 



their intimate association: the two chromosomes appearing on the first 

 maturation spindle are exactly the same as those which conjugated. 



