SEX-LINKED FACTORS IN DROSOPHILA 57 



POSSIBLE OBJECTIONS TO THESE RESULTS 



It will be noted that there appears to be some variation in 

 coupling strength. Thus, I found (CO)R to be 36.7; ^Morgan and 

 Cattell obtained the result 33.9; for OR I got 34.0, and for CR, 28.5. 

 The standard error for the difference between (CO)R (all figures) 

 and CR is 1.84 per cent, which means that a difference of 5.5 

 per cent is probably significant (Yule '11, p. 264). The observed 

 difference is 6.1 per cent, showing that there is some complication 

 present. Similarly, BjM gave 37.6, while OM gave 54.0 — and 

 BOM gave 36.7 for BM, and 36.5 for OM. There is obviously 

 some complication in these cases, but I am inclined to think that 

 the disturbing factor discussed below (viability) will explain 

 this. However, experiments are now under way to test the effect 

 of certain external conditions on coupling strength. It will be 

 seen that on the whole when large numbers are obtained in differ- 

 ent experiments and are averaged, a fairly consistent scheme 

 results. Final judgment on this matter must, however, be with- 

 held until the subject can be followed up by further expernnents. 



Another point which should be considered in this connection 

 is the effect of differences in viability. In the case of P and M, 

 used above as an illustration, the rudimentary winged flies are 

 much less likely to develop than are the longs. Now if the via- 

 bility of red and vermilion is different, then the longs do not give 

 a fair measure of the linkage, and the rudimentaries, being pi-esent 

 in such small numbers, do not even up the matter. It is probable 

 that there is no serious error due to this cause except in the case 

 of rudimentary crosses, since the two sides will tend to even up, 

 unless one is very much less viable than the other, and this is 

 true only in the case of rudimentary. It is worth noting that 

 the only serious disagreements between observation and calcu- 

 lation occur in the case of rudimentary crosses (BM, and (CO)M). 

 Certain data of Morgan's now in print, and further work already 

 planned, will probably throw considerable light on the question 

 of the position and behavior of this factor M. 



