40 



T. H. MORGAN AND ELETH CATTELL 



In this case the number of cross-overs is considerably smaller 

 than in the last, but since many classes are included and some 

 with high mortality the former estimate is probably more cor- 

 rect. 



If we add the two results together we get a total of 35496 

 counts in addition to the 474 cross-overs, which, on the basis 

 of calculations here employed, gives a ratio of 1 to 95. Whether 

 the difference in these ratios obtained at different times stand 

 for variations in the process itself, or whether they represent 

 chance results in the sense that for such a relatively rare event 

 the probable error will account for the differences can be more 

 profitably discussed at another time when the question of the 

 gametic ratios has been more fully studied. 



The gametic ratio of long and miniature wings versus red and 

 white eyes (LW and SR) gives more even results, because the 

 crossing-over is much more frequent and smaller numbers give 

 significant results. In our former paper ('12) there were 6829 

 cases of no crossing-over to 3573 cross-overs; a ratio of 1:1.8. 

 In the present paper there were 1835 cases of no crossing to 816 

 cross-overs; a ratio of 1:2.2. In the paper of 1911 there were 

 3177 cases of no crossing to 1713 cross-overs; a ratio of 1:1.8. 



Adding these cases together, the linkage ratio is 1: 1.94. This 

 means that the chance is about twice as great that the grand- 

 parental combination will hold as that it will break. These 

 results will need to be corrected for viability, and for other 

 disturbances as well, but there can be little doubt that the results 

 give approximately the gametic ratio for this combination. No 

 attempt has been made, here to separate those cases where LW 



