A. D. Darbishire. 
246 
inheritance of the two pairs of characters involved, considered 
separately. We know that Y is dominant to G ; and R to W. We 
know that in F 2 we get the proportions, in the one case 3Y : 1G ; 
and in the other 3R : 1W. We should therefore expect to get on 
the average, in every 16, 3 X 3—9 YR; 3 x 1=3 YW ; 1 X 3 =3 
GR and 1 x 1 =1 GW. 
These proportions are found to obtain in experimental results. 
I quote the results obtained by Mendel and Bateson. 
YR YW GR GW 
Mendel 315 101 108 32 
Bateson 4926 1656 1621 478 
It is customary to deduce these proportions from the contents 
of the gametes of the hybrids. It is evident, if we start with the 
assumption that a gamete can only bear one member of a single 
allelomorphic pair, but can be the bearer of any number of 
characters, so long as they belong to distinct allelomorphic pairs, 
that in the hybrids in question four kinds of gametes will be 
produced in equal numbers ; namely YR, YW, GR and GW. If 
one is asked why gametes with the formula of YG or RW or even 
RR cannot exist; the only answer which can be given at the point 
which we have now reached is that it is a part of the Mendelian 
theory (sometimes referred to as the doctrine of the “ purity of the 
gamete ”) that a gamete cannot bear both members of the same 
allelomorphic pair. This is of course not a satisfactory answer. 
But we shall see, at a later stage in the argument, that a satisfactory 
answer can be given. 
The manner in which the result in F 2 is brought about by the 
random union of the four kinds of gametes named above may be 
represented by a table similar to that on page 247. The four types 
of gametes borne by the male are written at the top, the four borne 
by the female at the left-hand side. The various types of the 
zygotes produced are given in the sixteen squares of the table ; 
below these formulae are written in italics, in each square, the 
somatic characters of these various zygotic types. 
It follows from the Table that only one of the 9 YRs are 
homozygous (DD) in both respects, viz: that in square a. 
Two are heterozygous (DR) for colour, but DD for shape, viz: c 
and i. Two are DD for colour, but DR for shape, viz : b and e. 
Whilst four are DR in both respects, viz : d, g,j and m. 
In the case of the 3 YWs and 3 GRs ; the W and the G in both 
cases are of course RR. 1 But of the 3 YWs the Y in two cases is 
1 It is, perhaps, hardly necessary to warn the reader not to confuse RR 
signifying Round-Round with RR signifying Recessive-Recessive. 
