Wright: Color Inheritance in Mammals 



479 



and Allen. *^ Spots on the back are 

 usually large — seldom less than one- 

 third "the total length of the back if 

 present at all. There is little or no 

 symmetry about the mid-dorsal line and 

 spots cross freely from one side to the 

 other. Certain kinds of spots are 

 unusual except in particular stocks in 

 which they may be common. Such are 

 a nose spot and a small rump spot. 

 Spots seldom cross the mid-line of the 

 belly but are sharply truncated by the 

 latter, a fact which strongly suggests 

 that the pattern is determined at a very 

 early stage of the embryo when the two 

 sides of the belly are as far from each 

 other as possible. In animals which 

 are largely colored the location of the 

 white areas is quite characteristic. 

 Thus white feet, white areas on the 

 nose and mid line of the face, on the 

 throat, narrow white streaks along the 

 under surface of the legs and along the 

 middle of the belly are especially 

 common. 



In tortoises the relation of red to 

 black is more nearly coordinate than 

 is the relation of white to color in pie- 

 balds, where, as just noted, it is dis- 

 tinctly a case of white gaps between 

 colored spots. The pattern is highly 

 irregular but a tendency may often be 

 noted to an arrangement of the colors 

 in relatively narrow alternate bands 

 across the back. The mid-line of the 

 belly breaks the continuity of the 

 pattern on each side as sharply as in 

 piebalds. 



INTERRELATIONS 



When both patterns, piebald and 

 tortoise, are combined,'^ it becomes 

 obvious that they are in some way 

 related in development. The spots are, 

 as a rule, either entirely black, entirely 

 red or entirely a kind of brindle or 

 brown. This, of course, would not 

 be the case if the patterns were simply 

 laid over one another. Again, there are 

 certain peculiarities within the spots 

 which prove an interrelation. Brindle 

 spots generally show more dark color at 



the center and thus vary from nearly 

 black with a brindle border to nearly 

 red with a brindle center. Another 

 fact which shows an interrelation of 

 piebald and tortoise is a curious sex 

 difference. Males, in general, show 

 slightly more color as opposed to white 

 and also more black (or agouti, etc.) as 

 opposed to red than their sisters. It 

 is not true in general, however, that 

 increase in white means increase in ratio 

 of red to black. In a given stock the 

 average ratio of red to black is remark- 

 ably constant for all grades of white. 

 In attempting to explain the relations 

 it is also to be noted that the presence 

 of piebald seems to affect the tortoise 

 pattern but not the reverse. The 

 localization of white seems to be the 

 same whether the spots are all black, all 

 red or some black and others red. The 

 tortoise pattern, on the other hand, 

 loses its tendency to narrow transverse 

 belts and conforms itself to the shape 

 of the colored spots. It may be added 

 that it is easy to make sketches of 

 piebalds and tricolors but tortoises 

 generally have such a jumble of small 

 spots and irregular brindling that a 

 satisfactory sketch is difficult to make. 



NO SAMPLE EXPLANATION 



It is evident that no simple explana- 

 tion of the determination of tortoise, 

 piebald and tricolor patterns can be 

 looked for. In piebalds there seems to 

 be involved some substance essential 

 for color production which has such a 

 relation to the latter that above a 

 certain critical level maximum color 

 production can take place, below it, none 

 whatever. Hereditary factors and, per- 

 haps, also environmental conditions 

 determine the general level in an animal 

 while various causes, hereditary or 

 otherwise, acting in development raise 

 or lower this level in different parts of 

 the coat, and so make possible a 

 pattern. In tortoise there seems to be 

 essentially the same situation with 

 respect to something necessary for the 

 production of black, except that the 



"Allen, G.M. 1914. .4 wer. iVa/., 48:385-412; 467-484; 550-566. 



15 Tricolors have been discussed by W. E. Castle, 1912, Amer. Nat., 46:437-440; A. Hagedoom, 

 1912, Amer. Nat., 46:682; Goodale and T. H. Morgan, 1913, Amer. Nat., 4/:321; and H. Ibsen, 

 1916, loc. cit. 



