NEW DATA. 



43 



In tables 14 to 17 the calculations for the three cross-over values for 

 vermilion, sable, and bar are given for the separate cultures and for the 

 totals. The latter are here repeated. 



The results of the different experiments are remarkably uniform. 

 There can be no doubt that the cross-over value is independent of the 

 way in which the experiment is made, whether any two recessives enter 

 from the same or from opposite sides. 



TABLE 18. Linkage of vermilion, sable, and bar with balanced viability. 



In table 18 the data from each of the four separate experiments have 

 been combined in the manner explained, so that viability is canceled 

 to the greatest extent. The amount of each kind of cross-over appears 

 at the bottom of the table. The total amount of crossing-over between 

 vermilion and sable is the sum of the single (9.53) and of the double 

 (0.28) cross-overs, which value is 9.8. Likewise the cross-over value 

 for sable bar is 13.49+0.28 ( = 14), and for vermilion bar is 9.53 + 13.49 

 ( = 23). By means of these cross-over values we may calculate the 

 coincidence involved, which is in this case 



0.0028X100 



= 20.8 



0.0953+0.0028X0. 1349+0.0028 

 This value shows that there actually occurs only about 21 per cent 

 of the double cross-overs which from the values of the single cross-overs 

 are expected to occur in this section of the chromosome. This is the 

 result which is to be anticipated upon the chromosome view, for if 

 crossing-over is connected with loops of the chromosomes, and if these 

 loops have an average length, then if the chromosomes cross over at one 



