No. 573] CHROMOSOME HYPOTHESIS OF LINKAGE 531 



as to the character of the chromosome, the average length 

 of the internode, and the percentage of chiasmas per node. 



Independence of Chromosomes I and II of Sweet Peas 



If two groups of genes are carried by separate chromo- 

 somes, we may expect to obtain free assortment and 

 typical 9:3:3:1 ratios in F 2 , when any two genes from 

 different groups are involved. There are rather extensive 

 data for three such cases in sweet peas, and in each there 

 is practically complete independence. The data given in 

 Table IV are summarized from Keport III to the Evolu- 

 tion Committee (page 37) and Report IV (page 17). 



The greatest departure from the 50 per cent, of cross- 

 ing over expected from independent assortment is only 

 to 47 per cent. 



There are several other characters whose genes seem to 

 be independent of those in the first and second chromo- 

 somes. This is interesting from the point of view that 

 each independent gene or group of linked genes requires 

 a distinct chromosome as a carrier. 



