Wright: Color Inheritance in Mammals 



477 



increase the extent to which a certain 

 relatively uncommon pattern, the col- 

 ored nose spot, was produced. A 

 similar differentiation in regard to 

 pattern has taken place automatically 

 among several families of very closely 

 inbred stocks which the writer is 

 studying. The very large amount of 

 variation in both amount and pattern 

 make Mendelian analysis difficult and 

 no unit differences have been thoroughly 

 demonstrated. The writer has, how- 

 ever, obtained rather clear indications of 

 segregation of a recessive unit factor for 

 piebald in crosses with a self-colored 

 feral stock and with a certain inbred 

 stock which is roan but not piebald. 

 Other nearly self-colored inbred stocks 

 behave very differently. That piebald 

 is inherited independently of the roan 

 variation is shown by a cross of a 

 uniformly piebald stock with the roan, 

 but not piebald, stock mentioned above. 

 Several, at least, of the young were 

 solid black, lacking both piebald and 

 roan, while the others approached this 

 condition very closely. 



ALBINO SERIES OF ALLELOMORPHS 



Albino guinea-pigs may show enough 

 black sootiness in the fur to bring out 

 clearly an underlying piebald pattern. 

 They generally have black points and 

 thus correspond best with Himalayan 

 rabbits. Castle^ found albinism clearly 

 recessive. Later^ he found a peculiar 

 series of varieties in Peru which seems 

 - to be unknown to American fanciers. 

 These had dark red eyes and white in 

 place of yellow in the fur but a fairly 

 intense black. An allelomorph of albi- 

 nism proved to be responsible for their 

 condition. The same variation seems 

 to have been obtained by Blaringhem 

 and Prevot^ from South America and 

 they were much puzzled by its mode of 

 inheritance. The writer found another 

 allelomorph in the series in the common 



dilute guinea-pigs in which intense 

 yellow or red is reduced to a lighter 

 yellow or cream and black is .slightly 

 reduced. Certain peculiar relations of 

 dominance within the series of four 

 allelomorphs were also found. ^ These 

 were discussed in the first paper of this 

 series. (Journal of Heredity 8:224- 

 235, May, 1917.) 



THE AGOUTI PATTERN 



Castle'^ early found the agoutis to 

 differ from the black and brown varieties 

 lacking this pattern by a unit dominant 

 factor. In ordinary agouti guinea-pigs 

 the belly appears yellow while the back 

 is black, each hair having a yellow band. 

 The width of the yellow band is quite 

 variable and w^hen narrow, black may 

 invade the base of the hair on the belly. 

 As in other cases, such variations may 

 be due either to variations in the 

 agouti factor itself or to independent 

 factors. In this case both have been 

 demonstrated. Thus the yellow band 

 increases greatly when black is weakened 

 by the action of the pink eye factor. 

 The same is true in the brindle spots 

 usually found in tortoise-shells. Thus 

 factors p and Ep can be looked on as 

 modifiers of agouti. Probably all fac- 

 tors of class 2 and perhaps some of class 

 1 in a more indirect way produce 

 variations in the width of the agouti 

 band. This effect seems to be through 

 weakening or reducing the amount of 

 black to be inhibited by the agouti 

 factor. A similar visible effect is pro- 

 duced by varying the strength of the 

 inhibiting agent itself and this is 

 presumably the mode of action of an 

 allelomorph of the factors for guinea-pig 

 agouti and nonagouti found by Det- 

 lefsen^ in hybrids between the guinea-pig 

 andC. rufescens, a BraziHan cavy. The 

 writer^ was able to confirm the existence 

 of these three allelomorphs but could 

 find no such difference between the 



3 Castle, W. E. and Allen, G. M. 1903. Proc. Am. Ac. Arts and Sci., 38:603. 

 ^Castle, W.E. 1914. Amer. Nat., 48:65-73. t 77 



5 Blaringhem and Prevot. 1912. Quoted by Lang, 1914, Experimentelle Vererhungslelire. 

 « Wright, S. 1915. Amer. Nat., 49:140-148, 1916, Cam. Inst. Wash. Pub., No. 241, part n, 



'Castle, W.E. 1905. Cam. Inst. Wash. Pub., No. 23, 7S pp. 1907. 5«. iV. 5., 25:151- 

 153. 1913. Cam. Inst. Wash. Pub., No. 179, p. 1-10, etc. 



8 Detlefsen, J. 1914. Cam. Inst. Wash. Pub., No. 205, 134 pp. 

 5 Wright, S. 1916. Loc. cit. 



