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A. D. Darbishire. 
“ germinal” feature is shared by Weismann’s theory of inheritance ; 
and is the most salient characteristic of the modern so-called neo- 
Darwinian view of inheritance. The question whether we should 
associate it with Mendel’s, or Weismann’s, or anybody else’s name 
has little interest for me ; but the reader who is curious on the point 
will find it briefly discussed in my first lecture. 
It has become customary to write the four possible types of 
union of gametes, and the zygotes resulting from them, in such a 
case as that which we have been considering, as follows:— 
Y x Y = YY 
Y x G = Y G 
G x Y = GY 
G x G = GG 
The formulae to the right of the equation marks may signify 
either the nature and number of the gametes borne by the zygotes 
produced by the union of the gametes to the left of the equation 
marks, or the somatic constitution of these zygotes themselves. 
The latter signification is preferable, because the former, by omitting 
the zygote altogether, commits one to a too dangerously unconditional 
belief in the theory of the continuity of the germ-plasm; and 
because the latter serves to lay emphasis on one conclusion 
reached by Mendelian analysis which is in accordance with cyto- 
logical knowledge. I refer to the conclusion that the zygote is a 
double structure whilst the gamete is a single one, which is in accord 
with the well-known fact that the number of chromosomes in the 
zygote is twice the number in the gamete. 
A very simple way of illustrating the results of the union 
of the gametes of two hybrids is to place in each of two 
hats, say, a hundred white and a hundred red counters, and a similar 
lot into another hat. The random union of the gametes can be 
imitated by drawing pairs from each hat, with eyes shut, and 
placing them in separate rows according as whether they are Red- 
White, Red-Red, or White-White pairs. The red counters may be 
placed on the top of the white ones to illustrate the dominance of 
red over white. The result will, on the average, be 25% RR, 
50% RW and 25% WW. The two kinds of zygotes which are 
produced in such a cross can be well illustrated by the means of 
these counters. A zygote which is the result of the union of similar 
gametes, i.e., a “red” with “red,” or “white” with “white” is 
called a homozygote ; of this there are two kinds, one in which both 
gametes are recessive, the other in which both are dominant. 
