67 
Inter-Relations of Genetic Factors. 
various reasons, the evidence to be gained from these cases is by 
no means conclusive, and the question must be left for further 
experiment to decide. 
The results outlined above open up several interesting problems, 
for a discussion of which the reader must be referred to Bateson and 
Punnett’s paper cited at the head of this article. It is only possible 
here to mention one or two more important points. In the first 
place comes the question as to how these gametic systems are 
formed. No simple system of dichotomies could provide the 
observed ratios, and it is scarcely possible to imagine bow a series 
involving 256 terms could be provided for in the maturation 
divisions of the ovary of such a plant as the Sweet Pea. There is, 
moreover, evidence from other sources which indicates that 
segregation may occur at an earlier stage than the actual divisions 
of sporogenesis or gametogenesis. 1 
Further, the fact that the heterozygote AB.ab shows coupling, 
while the heterozygote Ab.aB shows repulsion, suggests that the 
difference in behaviour may be a consequence of the difference in 
the geometrical positions of the factors relative to the planes of 
some critical division or divisions. If the original cell, in the 
divisions of which segregation takes place, be imagined to give rise 
to four quadrants, representing the four kinds of gametes, the 
increase in number of two of the types may be imagined as due to 
the proliferation of an opposite pair of quadrants, by a series of 
periclinal and anticlinal divisions such as would readily give the 
numbers characteristic of coupled systems. 3 If the numerical 
preponderance of two kinds of gametes be due to processes of this 
kind, it is clear that factors which are distributed according to one 
of these systems cannot be segregated simultaneously with other 
factors which are distributed on the normal Mendelian system. 
From what has been said above it is evident that the terms 
“coupling” and “ repulsion ” imply a conception which is no longer 
justified. “Coupling” was introduced to denote association, 
“ repulsion ” the disassociation of special factors. The phenomena 
are, however, now seen to be due to the production of an excess of 
certain kinds of cells, and Bateson and Punnett suggest that such 
cases may be conveniently referred to as the “ reduplication ” of 
certain terms in a series of gametes. 
In conclusion, reference must be made to the existence of 
systems of three factors. Cases are known in which two factors 
may be severally coupled with a third factor, and results of great 
interest may be looked for from investigations into the genetic 
properties of plants heterozygous for all three factors. 
R.P.G. 
1 E. R, Saunders. Rep. Evol. Com., Roy. Soc. IV, pp. 36—40, 
J908; Journ. Genetics, I, pp. 60—64 and p. 304, ff. 1911. 
de Vries. Biol. Centralbl., XXXI, p. 97, 1911. 
2 For a further explanation of this conception the reader is 
referred to Bateson and Punnett’s article in the Journ. 
Genetics, Vol. I, pp. 299 ff. 
