The Behavior of the Chromosomes as Studied through Linkage. 



241 



only, 



Table HI. 



The column headings below indicate the nature of the olasses obtained. 



- represents the non- cross -overs, | the cross-overs between the first two 



I the double cross-overs. 



"I those between the second two loci, and 



plementary classes (added together in table III, in the last column but 

 one): they are due to "double crossing- over" — to the chiasmatype 

 occurring twice in the same pair of chromosomes. 



It is apparent from these results that the occurrence of one cross- 

 over in a given chromosome pair tends to prevent the occurrence of 

 another one in that pair. Thus in the case of YWM, crossing over 

 between Y and W occurred in 1/69 of the cases when there was no 

 crossing over between WM, but in only about 1/441 of the cases where 



') The data for this combination are from Morgan 'lib, and Morgan and 

 Cattell '12, '13. The count on p. 395, Morgan 'lib, was omitted because of the 

 abnormally small size of the yellow white miniature class. That on p. 96, Morgan 

 and Catteli, '13, was omitted because it gave more double cross-overs than all similar 

 cultures combined. 



-) From Morgan '12b. 



The other six rows are either new or from Stürtevant '13. 



Induktive Abstiimmungs- und VererbungsU-hro. XIII. X7 



