FRAGMENTATION AND TRANSLOCATION 



315 



Fragmentation of Chromosomes. — A chromosome may sometimes be 

 "broken" transversely into one or more pieces. In the Hterature there 

 are numerous reports of small bodies interpreted as such "fragments" 

 of "normal" chromosomes, and in some of these cases the morphology of 

 the normal chromosome set is known well enough to render the interpreta- 



I 



\ Los^-A 



Losh-. 

 •1 Terminal delefion 



01 



2 In-hercalary dele+ion 



01 



01 



b 



c 

 ol 



3 Terminal inversion 



4 In-j-ercaloiry Inversion 



5 Simple +roinslocc«i'ion 6 Reciprocal +roinslocc5ition 



Fig. 179. — Diagram illustrating possible modes of origin of various chromosome abnormal- 

 ities. Spindle-attachment region indicated. {In part after Serebrovsky, 1929.) 



tion valid. The effects of such fragmentation on the appearance of the 

 chromosome complement are various. Sometimes the chromosome 

 number is apparently raised by one, since both pieces of the broken 

 chromosome are present (Fig. 198, F). Or, one of the pieces may be lost 

 (deleted) or inverted, so that the complement is still normal with regard to 

 number but abnormal in the morphology of one member. Again, a 

 fragment may be attached to another chromosome (translocation), so that 

 the number remains normal while the morphology of two members is 



