GAMETIC COUPLING AND REPULSION IN THE SILKWORM. 



upon the results of several matings from the various lots. On the whole these 

 experimental results set forth in the preceding pages are, as far as they go, 

 almost exactly what we should expect to get if our assumption is correct. 



Furthermore, though the numbers of the individuals reared were not 

 sufficiently large to determine the gametic series, I am inclined to think 

 that the partial coupling in my case was on the 7:1:1:7 system. The 

 actual figures are in fair accordance with the theoretical expectation on that 



As may be seen from what I have given in the historical review, partial 

 repulsion is less common than partial coupling. In plants the examples of 

 repulsion as yet known are for the most part perfect, while the majority of 

 coupling phenomena is partial. The same rule probably also holds good with 

 animals. At least with the Silkworm such seems to be the case, for I have 

 encountered here two examples of partial and one of complete coupling, 

 while the three cases of the repulsion were all complete. 



A striking fact has been found with regard to the genetic interrelation 

 of the striped marking and yellow colour. It is the occurrence of two 

 different systems of gametic coupling between these characters, a partial 

 coupling on the 7:1:1:7 system on the one hand, and a complete 

 coupling on the other. Batesox met with a similar case in the sweet pea, 

 where as a result of the partial coupling of the purple colour (i. e. the blue 

 factor) with the long pollen, he obtained the 7 : 1 series in F 2 of the cross 

 Blanche Burpee x Emily Henderson, while the F 3 offspring of the same 

 cross showed a closer agreement with the expectation on the 15 : 1 basis. 

 The latter system also appeared in F, of .the Bush x Cupid cross. The 

 question how such phenomena arise is not solved as vet. 



As to the adoption of the terms 'coupling' and 'repulsion', though their 

 appropriateness may be questioned, yet I prefer from the following reasons 

 to preserve them in their original sense: 1) the terms are already widely 

 accepted, 2) to keep the 'coupling' distinguished from 'repulsion' is at least 

 convenient, because the F. phenotypic ratios resulting from them are funda- 

 mentally different. The term 'reduplicated system' may be conveniently 

 used as a general name including both coupling and repulsion. 



