COLOR AND COAT CHARACTERS. 35 



HETEROZYGOTES FOR EXTENSION MATED INTER SE. 



Only 14 matings were made in which both parents were known to be 

 heterozygous in extension (table 43). The wild hybrid females used 

 ranged from I wild to -g^ wild. The male parent was in every case a 

 guinea-pig. In these matings each parent is expected, on MendeUan 

 principles, to produce, in equal numbers, gametes carrying extension 

 and gametes without that factor. The chance combinations of such 

 gametes should give two visible classes, in the ratio of 3 : 1. The actual 

 results were 45 of extended pigmentation and 13 of restricted pigmen- 

 tation, which is very close to the most probable expectation. The 

 hybrid females therefore form two kinds of gametes, just as guinea-pigs 

 do ; and the usual 3 : 1 ratio results from mating a heterozygous hybrid 

 with a heterozygous guinea-pig. 



REDS MATED INTER SE. 



The fact having been established that red is a recessive character 

 among the hybrids as among guinea-pigs, it would seem to be scarcely 

 necessary to show by breeding test that reds produce only red-colored 

 offspring. Nevertheless, three matings have been made between red 

 hybrid females (290, 291, and 292) and a red guinea-pig male (67). 

 These matings produced 4 offspring, all red.^ 



7. COLOR AND ALBINISM. 



HOMOZYGOUS CONDITION OF THE COLOR FACTOR IN CROSSES. 



Albinism is common among domesticated rodents. It has been 

 shown to be allelomorphic to color in mice, rabbits, rats, and guinea- 

 pigs. Recently, Castle (1912) reported a case in which a wild albinic 

 sport of Peromyscus was mated to normals, and by mating a normal 

 Fi female back to the albino father, normal and albino F2 offspring were 

 obtained. Albinos are not known among any wild cavies. The expla- 

 nation for the albinic condition on a factorial basis suggested by 

 Cu6not (1903) is now generally accepted. This explanation postulates 

 a color factor, C, which is necessary for the development of color 

 in the eye, hair, and skin; and the entire absence of this factor (des- 

 ignated by c) results in albinism. Among rabbits, two sorts of 

 albinos are recognized, the ordinary and the Himalayan albino. The 

 latter condition is distinct, for a small amount of pigment is present 

 in the hair of the nose, ears, and other extremities; and this condition 

 is epistatic to ordinary albinism. It may be necessary to assume a 

 different factor, such as C, for the Himalayan condition, in place of 

 c, which is used for the ordinary albino. In this case, C would be 

 allelomorphic to C or c, just as A' has been shown to be allelomorphic 



'Since the foregoing was written a similar result has been obtained from additional matings, in 

 some of which the male parent was indeed a fertile hybrid. 



