192 MENDELISM 
stances the heterozygote is found to exhibit an appear- 
ance which is more or less intermediate between the 
types of character shown by the parents. It may be 
almost exactly intermediate, or the appearance of the 
cross-bred form may be nearer to that of one parent 
than to that of the other. Dominance is clearly only 
an extreme case of this latter phenomenon. The 
term ‘dominance’ is applied to those cases in which 
the appearance of the hybrid offspring is so near to 
that of one parent as to be no longer clearly distin- 
guishable from it. 
In other cases, still of a simple Mendelian nature, 
the appearance of the heterozygote may be quite 
different from that of either parent homozygote. An 
excellent example which is almost certainly of this 
nature is afforded by the Andalusian fowls studied 
by Messrs. Bateson and Punnett. And this will also 
serve as our first illustration of the application of these 
principles to animals as well as to plants. The facts 
of the case are as follows : 
The ‘blue’ type of Andalusian appears to be a 
heterozygote form which has never been got to breed 
true. When a pair of these birds are mated together 
only about half their offspring are like themselves, the 
remainder being entirely different. Half these re- 
maining ‘wasters’ are black, and half are nearly 
white, showing only a few black ‘splashes.’ If, now, 
a pair of the black wasters are mated together, they 
breed perfectly true, yielding only black offspring like 
themselves. Similarly the splashed whites mated 
together give rise to splashed white, and nothing else. 
