1202 BIOLOGICAL EFFECTS OF RADIATION 



is low in frequency in the vicinity of the spindle attachments. The 

 results of Beadle and of others who have studied the linkage relations 

 in individuals homozygous for chromosome rearrangements prove then 

 that the distribution of crossing over along the chromosomes (as studied 

 through the cytological maps) is not a property of the substance of the 

 chromosome located in its various parts, but rather the result of the 

 mechanical relationship leading to crossing over, in which the spindle 

 attachment plays a role. 



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