X§4 GENETIC STUDIES ON THE SILKWORM 
Heterozygous males used in above crossings were taken from various lots 
of the F-p F 3 or F 3 generation derived from the cross striped yellow x 
normal or plain or quail or pale-quail white, and all the families mentioned 
showed more or less approximation to a definite ratio of phenotypes. It is 
therefore obvious that in heterozygous striped yellow males a partial coupling 
denoted by the formula 3 : 1 : 1 : 3 or the like takes place between striped 
and yellow factors. 
4) Discussion. 
In the cases of coupling and repulsion described in the foregoing pages, 
there is little doubt that two ancestral forms only occur in equal numbers in 
F x oogenesis, no "cross-over" being produced. On the other hand, F 1 male 
gametic series shows, when each family is taken separately, a good deal of 
variability. When, however, a number of families are mingled together the 
ratios seem to converge to the formula 11 : I : I : n for coupling and / : 11 : 
11 : 1 for repulsion, where represents a number ranging from 2.5 to 3.0. A 
similar variability of association intensity is also met with in Drosophila, in 
even higher degree, as can be seen in the paper of Bridges and Sturtevant 
( 1 9 1 4) . In the test of F x females from the cross black x curved, they reared 
14 families, in which the percentage of cross-overs varied from 15.2 to 31.6 
(/. c. p. 209) according to families. 1 5.2 % of cross-overs corresponds to 1 : 5.6 
: 5.6 : 1, and 31.6% corresponds to 1 : 2.2 : 2.2 : 1, on the assumption that 
the gametes are symmetrically distributed. A similar phenomenon occurred 
in experiments of Gregory on Primula ( 1 9 1 1 a, especially see pp. 127-129) 
and in those of Punnett on the sweet-pea (191 3, especially see p. 86, Tables 
II and IX.) 
From the literature on gametic reduplication we learn that the association 
was proved to be of the same intensity in both sexes of certain plants; the 
method of proof adopted being the crossing of the hybrids with double 
recessives. PüNNETT (191 3) proved, for instance, such an association in 
the coupling (7 : 1 system) of blue factor and long pollen in the sweet-pea, 
