70 



MITOSIS : THE VARIATION OF THE CHROMOSOMES 



readily visible in mitotic chromosomes are necessarily restricted to 

 four types ; first, independent changes of size that may be attri- 

 buted to loss or gain following deficiency or translocation ; secondly, 

 related changes of size in two chromosomes such as may be attributed 

 to translocation or interchange between them ; thirdly, changes in 

 the position of the centromere that may be attributed to inversion 



Table 8 

 Analysis of Variation in Crepis 



* Different series of observations. 



t One was trisomic. 



X Also showed fragmentation. 



of the segment containing it ; lastly, changes in number of chromo- 

 somes that may be attributed to fusion and fragmentation pro- 

 visionally, but which must be due to secondary charges following 

 interchange, since with normal monocentric chromosomes a change 

 in the number of chromosomes means a change in the number of 

 centromeres. Such a secondary change will usually have occurred 

 as a result of the recombinations at meiosis which we shall consider 



