Autotetraploids 



447 



autotetraploids if they are found. Tradescantia affords some 

 good examples of quadrivalent formation in autotetraploids. An- 

 derson and Sax have said that more than half the chromosomes 

 are in quadrivalents in autotetraploids in this genus and that 



iin 



1 1 

 I i 





^3C 





Fig. 127. Some of the configurations formed in a tetraploid when there 

 are fewer than four chiasmata. Below each diplotene configuration is the 

 metaphase to be derived from it. Top line, (a), (b), (c) ; middle line, (d), 

 (e), (/) ; bottom line, {g), (h), (?). 



they are usually in the form of chains or rings. The chiasma 

 frequency per chromosome is lower in the tetraploids than in 

 the diploids, and almost all the chiasmata are terminal in the 

 tetraploids. In T. virginiana some quadrivalents are twisted 

 around so as to resemble the number ''8," and usually the adja- 

 cent chromosomes in the quadrivalent pass to opposite poles. In 



