THE CHROMOSOME HYPOTHESIS OF LINKAGE 

 APPLIED TO CASES IN SWEET PEAS 

 AND PRIMULA 



CALVIN B. BRIDGES 



There are two views as to the nature of linkage. The 

 earlier view, developed by Bateson and his co-workers, is 

 that this phenomenon is an expression of symmetrical 

 reduplications in the germ tract. A more recent view, 

 developed by Morgan and his co-workers, treats linkage 

 on the basis of a linear arrangement of genes in the 

 chromosomes and of the history of these genes during 

 normal gametogenesis. The advocates of the reduplica- 

 tion view have rarely applied their principles to the re- 

 sults on Drosophila on the ground that the results for 

 Drosophila are complicated by sex-linkage. That sex- 

 linkage is simply an additional, but wholly independent, 

 phenomenon, is proven by the many cases in DrosophUa 

 in which sex-linkage is not involved, yet in which the link- 

 age of the genes to each other is of the same type as the 

 linkage of sex-linked genes to each other. 



In this paper I shall attempt to show, that the theory of 

 linkage which we have successfully applied to all cases in 

 Drosophila, whether involving sex-linked genes or genes 

 which show no sex-linkage, applies equally well to the 

 non-sex-linked cases occurring in sweet peas and primula. 

 The only serious drawback to such an application lies in 

 the nature of the data which have been collected for these 

 cases. The least satisfactory form of data from which to 

 determine a linkage value is that presented by F 2 results. 

 In cases in which two recessives enter from opposite par- 

 ents ("repulsion"), the excessive smallness of the double 

 recessive class' in F 2 renders any calculation subjei t to irivat 

 error. Slightly better are the F a results from coupling. 



