EPISTATIC CHARACTERS 207 
only four types of colour—the ‘ agouti’ or wild grey 
colour, black, ‘ chocolate,’ and albino. The behaviour 
of these colours in heredity can be described in terms 
of three pairs of allelomorphs : 
Gg: The presence and absence of the factor which 
gives the ‘ agouti’ or grey pattern in the hairs. 
Bb: Presence and absence of the black determiner. 
Cc: Presence and absence of colour. 
Where C is present without G or B, the colour is 
chocolate, the proper formula for such an animal 
being CCggbb or Cceggbb. Black mice may be CCggBB, 
etc., and grey mice CCGGBB, etc. 
All albino mice are to be represented as those from 
which C—+.e., the chocolate colour—is absent ; but 
either G or B, or both, may be present (but masked) 
in an albino individual. 
When B and C are both present, the colour is black, 
and not chocolate. We cannot, however, speak of 
black as being dominant to chocolate, since these two 
factors belong to independent allelomorphic pairs. A 
new term is therefore required for this relationship, 
and also for the relationship between grey and black. 
Bateson’s suggestion for the required terminology may 
be given in his own words: ‘ We can, perhaps, best 
express the relation between the grey and the black 
by the use of the metaphore “ higher and lower,” and 
I therefore suggest the term epistatic as applicable to 
characters which have to be, as it were, lifted off in 
order to allow the lower or hyfostatic character to 
appear.” Thus grey is epistatic to black, and black 
is epistatic to chocolate.‘ 
