70 GENETIC VARIATIONS 



In other cases the middle piece drops out entirely and is 

 lost. The two end pieces then reunite at their broken ends. 

 Thus a short chromosome is produced, lacking all the genes 

 of the middle region, but still carrying those near the two 

 ends (Figure ii, C). These are known as deletions — the mid- 



Aabcdeighij klmtio 



B 



abcdihgfejklmno 



■« • • • [ 9 • • • » I m • • 9 • •- 



a bcdj k Imno 



-• • • • • • • • •- 



D 



Figure ii. Diagram of changes in the order or arrangement of the 

 genes in consequence of breakage of chromosomes. A. Part of a chrom- 

 osome with genes a to o in the normal order, B. Inversion: the genes 

 between d and ;' are reversed in their order. C. Deletion: the genes 

 e to / have dropped out. D. Genes of two chromosomes. E. Transloca- 

 tion: the two chromosomes of D have exchanged certain portions. 



