2 Results of Crossing Grey [House) Mice ivitJi Albinos 
Cu^not ('04) suggests that all mice, including albinos, have some definite 
colour in them, but that it needs a special faculty to make this latent colour 
apparent on their coats, and that the difference between all coloured mice and 
all albino mice lies in the possession or non-possession of this faculty. 
Coat-colour, then, is a compound character which must be split up primarily 
into two component parts: (1) nature of the colour; (2) power, or lack of power 
of producing colour. He represents the constitution of the gametes of a mouse 
with regard to these two things by two letters, the first indicating their condition 
with regard to (2). When they are colour-producing the letter G (chromogene) 
is used, when non-colour-producing A (albino). The second letter denotes the 
nature of the colour. Thus G grey, B black, and Y yellow. 
For example : 
GG represents an ordinary house mouse. 
AG represents an albino mouse whose gametes would produce the grey colour 
if possessed of the colour-producing faculty. 
GB = {i pure black mouse. 
AB a mouse similar to AG, only with Black for the latent colour. 
CY a pure yellow mouse. 
AY albino with yellow latent. 
The six symbols described above denote six pure races of mice. When any 
two of these are mated together hybrids will of course result whose gamete formula 
is a combination of the gamete formula of the two parents. The colour of the 
hybrids is determined by the relative dominance : (1) of colour productiveness and 
albinism ; (2) of the nature of the two colours latent in the two parental gametes. 
As in all cases colour dominates albinism, it only remains to be considered which 
of the three colours employed is dominant over which of the others. Here we 
find G dominant over B, Y dominant over B, Y dominant over G. Thus a grey 
GG crcssed with a white AY will produce yellow mice whose formula is GG-AY. 
A black GB crossed with either a grey GG or a w^iite AG will produce grey mice, 
though in the first case the formula will be GB-GG, and in the second it will be 
GB-AG. 
All this is not a modification nor an extension of Mendel's laws, but merely an 
application of them to a special case ; Cuenot's theory as to the two factors which 
determine coat colour rendejs such an application possible. The further behaviour 
of the hybrids when crossed among themselves or with pure mice can therefore be 
predicted by any one conversant with these laws and possessed of a knowledge of 
the gametic formula of the hybrids used. 
A third element is introduced by the fact that the colour of a mouse's coat»is 
not always uniform, but may be marked with white. This marking may occur 
with mice of any colour ; it is transmitted independently of the colour, and may be 
latent in albinos. A uniform coat dominates a piebald coat. 
Thus if one mates a piebald yellow mouse with an albino with uniform greyuess 
