GAMETIC COUPLING AND REPULSION IN THE SILKWORM. 
125 
It is evident from the above result that a complete repulsion took place 
between stripedness (S) and normalness (N). The gametes produced by these 
Fj striped yellows (SnYsNy) must have been, therefore, of only four kinds 
as follows : 
SnY, sNY, Sny, sNy. 
By random combination of these gametes there must arise four F 2 forms — 
as observed in the experiment — striped yellow, striped white, normal yellow 
and normal white, in the ratio of 9 : 3 : 3 : 1. This normal ratio is, 
however, disturbed in the present case by virtue of partial coupling taking 
place between the striped and yellow factors, the detailed statement of which 
is given in the following pages. 
V. Gametic Coupling. 
Two cases of partial and one example of complete coupling were observed 
in my experiments. 
A. Partial coupling. 
I. Partial coupling between stripedness (S) and yellowness (Y). 
a) The hereditary behaviour of the Fj striped yellow SnYsNy just 
referred to above (H. 1. ’ll) clearly points to the conclusion that there 
occurs a partial coupling between striped marking and yellow colour, as 
may be seen from the following consideration. 
If we take for granted that a perfect repulsion occurs between striped 
and normal character in the F, striped yellows, we should obtain four F 2 
forms in the ratio 
9 striped yellow 
3 striped white 
3 normal ytllow 
1 normal white. 
