No. 573] CHROMOSOME HYPOTHESIS OF LINKAGE 527 



The gene for red is then about eleven units from that for 

 round, and the gene for hooded is nearly one unit from 

 that for red. 



TABLE I 

 Chromosome I 

 Round Pollen and Red Color 



Coupling ...7,897 583 614 2,197 .9596 7.9:1 11.2 



The order of arrangement of these genes in the chromo- 

 some can be discovered from a comparison of the linkage 

 values found above. The linkage value (11.2) for round 

 and red is the most accurately determined of those in- 

 volved, so that we may lay this down as our initial or 

 base line: 



The next most accurate value is that for red and 

 hooded, namely, 0.8. Hooded lies therefore only about 

 one unit from red, but if these two values only, namely, 

 round red and red hooded, were given, we should be un- 

 able to decide whether h<m<led lies between round and red 

 at a position near 10 (that is, 11.2 — .8) or beyond red in 

 a locus at 12 (that is, 11.2 -f .8). In order to determine 

 whether hooded lies to the left or to the right of red the 



