400 Intrachromosomal Aberrations 



If the inversion includes the centromere and there is one cross- 

 over within it, dicentric chromosomes and fragments are not to 

 be found, but only two of the resulting four chromatids are nor- 

 mal. One of the chromatids will be duplicated for one of the 

 segments not included in the inversion and will be deficient for 



Fig. 106. Chromatid bridges and a fragment in a triploid natural hybrid 

 between Tradescantia paludosa and T. canaliculata. Three of the 18 

 chromosomes are not shown in the photomicrograph. One long bridge 

 with a fragment is approximately in the center of the figure, and the other, 

 a much shorter bridge, is to one side. 



the other; the fourth chromatid will be deficient for the first 

 segment and duplicated for the other. Because of the presence 

 of loops at zygotene or in salivary gland chromosomes and of 

 chromatid bridges and fragments at anaphase in natural popu- 

 lations, the possibilities to be realized in inversion heterozy- 

 gotes should be understood. 



Plants or animals homozygous for an inversion do not present 

 the same problems that we find in those that have only one 

 chromosome with an inverted segment. No loops are observed 



