Mr Doncaster, On the Inheritance of Goat-colour in Rats. 215 



On the Inheritance of Coat-colour in Rats. By L. Doncaster, 

 M.A., King's College. 



[Received 29 November 1905.] 



In July, 1903, I began breeding-experiments with the various 

 colour-varieties of the Common Rat, with the intention of working 

 out the laws of their inheritance. At that time Cuenot's later 

 papers on Mice bad not yet appeared, and my chief object was to 

 investigate the " resolution " which appeared to take place when 

 the wild brown rat is crossed with the albino. In the wild 

 brown (or grey) rat there are three pigments, black, brown, 

 and yellow, as there are in the common mouse ; but among the 

 descendants of a wild rat crossed with an albino, black animals 

 containing no "yellow pigment commonly appear*. The chief 

 object with which I began the work was to determine if possible 

 how this suppression of the yellow took place, and why the 

 corresponding disappearance of black, which occurs in mice, is not 

 found in rats. 



The colour varieties of rats have been described and classified 

 by Crampe-f-, and again by Bateson (loc. cit. p. 78). They are 

 much simpler than in mice, so that a rat which does not fall 

 unmistakeably into one of Crampe's seven categories is extremely 

 rare. In colour all the rats which I have bred have been either 

 brown (wild colour), black, or albino. The brown rat is darkest 

 along the back, has a considerable number of hairs with yellow 

 tips on the sides, and is pale grey below. The black is full black 

 everywhere when the animal is young, but as it grows older, 

 especially when moulting, it tends to a chocolate-brown tint on 

 the sides and ventral surface, but has no trace of yellow. The 

 albino is quite white when young, but inclines to a cream tinge 

 Avhen older. Albinos have pink eyes, coloured rats black. Both 

 the brown and black rat may be quite without white except 

 on the toes, which are never pigmented (Crampe's types 1 

 and 7), they may have a patch of white of varying size on the 

 chest and belly (types 2 and 6), or they may have a coloured 

 " hood " and stripe along the back, the rest being white (types 3 

 and 5). Crampe's type 4 is the albino. Types 2 and 6 vary 

 within rather wide limits ; the white mark on the chest may be 

 limited to a few hairs, or it may extend into a broad white ventral 

 surface, sometimes spreading slightly out to the flanks. The tail 



* The distribution of the pigments in the hairs I find to be identical with that 

 described by Bateson in Mice (P. Z. S. 1903, n. p. 72); the black rat differs from 

 the brown in the absence of yellow pigment. 



f "Kreuzungen zwischen Wanderratten," Landwirtk. Jahrb. vi. 1877, p. 384; 

 xn. 1883, p. 389; xin. 1884, p. 692. Also "Die Gesetze der Vererbung der Farbe," 

 ibid, xiv. 1885, p. 539. 



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