i6o 
GENETIC STUDIES OX THE SILKWORM 
Now if we assume the F x gametes as 
PÖY Pfty PqY Pqy 
Eggs i : o : o : I 
Sperm. 3:1:1:3 
the succeeding zygotic series ought to be 
11 : 1 : 1 : 3. 
Comparing this ratio with my actual F a counts in 19 14, we obtain 
Norm. yel. Norm. wh. PI. yel. PI. wh. Totals 
Spring 1 91 4 2338 282 212 636 3468 
Summer 1914 214 15 19 51 299 
Totals 2552 297 231 687 2,767 
Expect. 2590 235 235 706 3766 
The theoretical figures are not far from the actual ones. 
We can, however, assume another ratio, 5:2:2:5 (2.5 : 1 : 1 2.5); 
on this basis the zygotic ratio and calculated numbers are 
Norm. yel. Norm. wh. PI. yel. PL wh. Total 
Ratio 19 : 2 : 2 : 5 28 
Expectation 2556 269 269 673 3767 
It follows that, as in the case of repulsion, there is room for doubt as to 
the actual system of coupling in the male hybrid. Moreover, the zygotic 
proportions in various lots are not quite identical : whether such a fluctuation 
is or is not due to chance is to be decided by further experiments. 
All individuals concerned in the above experiments were homozygous for 
the presence of P factor. Now I am to describe the cases in which the domi- 
nant individuals were homozygous for the absence of P, or were heterozygous 
for P. The results are quite the same with those given above, so far as the 
0,-Y coupling is concerned. 
Triply heterozygous normal yellows (PQYpqy) 
mated inter sc. 
A 452'! 5 A 4 53'i5 A 454'! 5 A 456'! 5 Totals 
Normal yellow PQY 143 169 146 147 605 
Normal white PQy 9 14 22 21 66 
