480 



The Journal of Heredity 



critical level is not so sharji. There is a 

 zone between red and black in which 

 brindle or brown may appear. The 

 variation in both patterns from a hi^'h 

 dej:;ree of symmetry with respect to 

 the parts of the body to a condition of 

 asymmetry which almost wholly dis- 

 regards the latter, points to a com- 

 plexity of causes. Perhaps time is a 

 factor — pattern differentiation, which 

 arises very early, tending,' to be imrclated 

 with the later symmetrical differentia- 

 tion cjf the embryo and vice versa. In 

 this connection it is interesting^ to note 

 that in some jiiebald mammals as rats, 

 raV)bits and Hereford cattle there is a 

 high degree of symmetry, while others as 

 mice and Holstein cattle approach closer 

 to the chaotic patterns of guinea-pigs. 



In the relations of the ])atterns to 

 each other, there are all variations from 

 independence to obvious coordination. 

 The main genetic factors, as S and Ep, 

 seem to be inherited independently, 

 other factors, of which sex is one, act 

 on both patterns, perhaps through some 

 general influences on metabolism, and 

 doubtless there are both independent 

 and common nongcnctic factors which 

 act during develo])mcnt. Among the 

 latter must be considered the possibility 

 that mutations in the hereditary ma- 

 terial received from the zygote may 

 take place at random in the somatic 

 cells producing spots in the groups of 

 cells which descend from them. Differ- 

 entiation due to such a cause would 

 produce a mosaic of coordinate black, 

 red and white spots. On the other 

 hand, the general relations of color to 

 while and also of black to red in the 

 case of a dark spot with a red border 

 surrounded by white suggest the radia- 

 tion of some influence from centers in 

 the skin, with simultaneous effects on 

 both the level for i)igment production 

 and for black. 



Summing u\), it ai)i)ears that coat 

 pattern in guinea-])igs, and doubtless 

 other animals as well, must be deter- 

 mined by a complex of causes of very 

 diverse kinds.' There are hereditary 

 factors of various sorts and factors 



which are of the nature of accidents in 

 development. There arc factors which 

 aflect the extent of pattern and others 

 which determine its localization. Of 

 the latter some relate the pattern to the 

 axis of symmetry and organs of the 

 body while others are random in their 

 incidence. Some factors affect only 

 the tortoise pattern in one way or 

 another, or only the piebald pattern, 

 while others have a simultaneous in- 

 fluence on both. The result is such a 

 diversity of ])attem among tri-colors 

 that a rough sketch will identify almost 

 any animal in a stock of a thousand. 



OTHER VARIATIONS OF GUINEA-PIGS 



Black sootiness often appears in the 

 red or yellow parts of the fur of guinea- 

 pigs as they grow older. This sootiness 

 is cs]3ccially conspicuous in i)ale creams 

 and in whites resulting from extreme 

 dilution of red (CrCr). As such sooti- 

 ness never appears in the white ])arts 

 of piebalds, its presence gives another 

 means of distinguishing white spots 

 which represent reduced red from pie- 

 bald white, besides the different appear- 

 ance mentioned above. The mode of in- 

 heritance of black sootiness is unknown. 



Two independent Mendelian factors 

 are known which dilute l)lack \-cry 

 uniformly throughout the skin, fur and 

 eyes, but have no influence on the 

 intensity of red. The first of these to 

 be known ^^ changes black to brown, 

 ordinary agouti to cinnamon, black 

 and red tortoise to brown and red 

 tortoise, black-eyed red to brown-eyed 

 red. etc. The other is responsible for a 

 series of pink-eyed colored varieties 

 unknown to the fanciers. The latter 

 was found by Castle'' in one of the 

 South American stocks which also 

 furnished the red-eyed dilution. The 

 eye generally shows traces of pigment. 

 Black in the skin and fur is reduced to a 

 very ])ale brown, much ])aler than in 

 the brown varieties while red is unaf- 

 fected in intensity, lioth the brown 

 factor, b, and the ])ink eye factor, p, are 

 Mendelian recessives and both obviously 

 belong in class 2b. 



'• Castle, W. E. 1007. Set. N. S., 26:287-291; 1008, Sci. N. S., 28:250-252. 

 "Castle, W.K. 1014. Lor.fit. 1016. Lnc.cit. 



