'54 
GENETIC STUDIES ON THE SILKWORM 
Norm. yel. 
Norm. wh. 
PI. yel. 
PI. wh. 
Totals 
H 43-i''3 
39 
1 17 
121 
40 
317 
ri 4j 2 1 3 
34 
04 
70 
37 
211 
I 1C> 
I 1A 
1 J^f 
ft 
ICO 
P 62'i4 
49 
208 
157 
36 
450 
P6;'i 4 
46 
133 
139 
38 
356 
P 68'h 
70 
175 
129 
27 
401 
Totals 
280 
827 
756 
22 2 
2085 
Thus a partial repulsion occurred in F x males instead of the complete one 
that took place in females of the same generation. As to the intensity of 
repulsion there is some fluctuation which makes it impossible at present to 
determine exactly the system of reduplication. For instance, H43-i'i 3 shows 
a phenotypic ratio close to 1 : 3 : 3 : 1, whereas H 43-2' 1 3 rather approaches 
to 1 : 2 : 2 : 1. In other lots there are found similar variations in the 
zygotic ratio, that is the gametic ratio of the heterozygous parents. The 
theoretical numbers calculated on the 1:3:3:1 basis are compared with 
the actual results : 
Normal Normal Plain Plain Total 
yellow white yellow white 
Observed 280 827 756 222 2085 
Expected 260.6 781.9 781.9 260.6 2085.0 
The present case affords a strong basis for the argument that the cross- 
ing of F x individuals with double recessives not only facilitates the study of 
gametic distribution, but is indispensable for it, as has been repeatedly stated 
by various authors. But the results of mating various phenotypes among 
themselves also throw some light upon the subject, though the actual feature 
of gametic distribution is not fully manifested in this way alone. 
If the Q.-Y relation be of the ordinary kind of complete repulsion, all F 2 
normal yellows should be heterozygous, to be split again in F 3 into three 
phenotypes, while the normal white and plain yellow offspring should neces- 
sarily be homozygous and breed true — processes to be effected in subsequent 
generations. But this expectation was not realised in my experiments, as is 
obvious in the following pedigree. 
