Inter-Relations of Genetic Factors. 
6 5 
of heredity in the Sweet Pea, it became clear that in certain cases 
there was a departure of a definite kind from this simple numerical 
relation. Eventually it became clear that this departure was such 
that the hybrid must be regarded as producing the four kinds of 
gametes in proportions represented by one or other of the series 
3AB : lAb : laB : 3ab 
7AB : 1 Ab : laB : 7ab 
15AB : lAb : laB : 15ab 
or generally 
(n—1) AB : lAb : (n—1) ab 
where “ n ” is a power of 2. 
Here, then, the gametes containing both factors are produced 
in greater numbers than those containing one or other but not both; 
this phenomenon was termed “ partial gametic coupling ” of the 
factors. 
At the same time other cases were being discovered in which 
it appeared that the hybrid produced only two kinds of gametes, 
namely Ab and aB, each containing one, but not both, of the 
factors, which apparently never passed together into the same 
germ cell. This phenomenon was spoken of as “ repulsion ” or 
“ spurious allelomorphism ” between the factors. The offspring of a 
hybrid in which repulsion is taking place should be of three types, 
namely AaBb, AAbb and aaBB, which should occur in the ratio 
2:1:1; since every gamete contains one or other factor, there 
should be no offspring of the type aabb. In several cases the 
results observed in large families conformed to these requirements; 
there were, however, one or two cases in which an isolated or 
occasional example of the double recessive, aabb, was encountered 
among the F a -individuals. Speaking of certain of these cases, Bateson 
and Punnett 1 say “ We incline to think .... that upon occasion the 
repulsion between factors may be imperfect, though whether this 
imperfection is sporadic, or whether it can be conceived as part of 
some scheme we do not yet know enough to say.” 
The next step was the discovery that the factors, A and B, which 
under certain circumstances are coupled, may under other circum¬ 
stances be repelled in the gametogenesis of the hybrid ; and it 
became clear that this difference in behaviour depends upon the 
distribution of the factors in the gametes to which the hybrid owes 
its origin. If the heterozygote, AaBb, is formed by the union of 
gametes, AB and ab, partial coupling occurs between A and B; if 
the heterozygote, AaBb, is formed by the union of gametes Ab and 
aB, repulsion takes place. For all cases of coupling, which it has 
been possible as yet to test, repulsion has been proved to occur 
when the cross is made in the appropriate form ; there still remain, 
however, several cases of repulsion which cannot yet be tested for 
coupling for lack of material, since the double recessive type, aabb, 
required for use as one of the parents, has not yet been 
encountered. 
So far, although coupling had obviously shown itself to be 
partial, the results had suggested that repulsion, with a few sporadic 
exceptions, was complete. During last summer, however, a case 
1 “ The Inheritance of the Peculiar Pigmentation of the Silky 
Fowl.” Journ. Genetics, I, p. 200, 1911. 
