36 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



to A or a in the modified wUd-agouti crosses. Albino individuals occur 

 in nature from time to time in many species, but it is supposed that 

 their conspicuousness in most cases renders them an easy prey to their 

 enemies. Albino guinea-pigs are always Himalayan. 



The old original wild male (cf 1) was bred to three albino guinea-pig 

 females; his son (cfSS) was also bred to an albino. Altogether such 

 miatings produced 18 young (table 44), all of which were normally 

 colored. It is probable from this, and from the records of the wild bred 

 inter se, that aU of the C. rufescens used in this experiment were homo- 

 zygous in the color factor. Early deaths and sterility prevented the 

 use of the offspring recorded in table 44, in further experiments; but 

 there is little doubt that the animals thus produced were heterozygous 

 in the color factor, with formula Cc; for in mating other | wi'd f'emales 

 to guinea-pig ma^es which lacked the color factor, young with a 

 formula Cc, were produced. 



A number of | wild females which were homozygous in color were 

 mated to guinea-pig males which lacked color entirely or were hetero- 

 zygous in it (table 45), producing 27 colored young. Just as the pure 

 wild C. rufescens color factor is epistatic to its absence in the guinea- 

 pig, so the i wild which had received one dose of the color factor from 

 C rufescens and one dose from C. porcellus were dominant in crosses. 



Table 46 shows the complete dominance of color over the albinic 

 condition in all the remaining blood-dilutions. In these matings, one 

 parent was homozygous in the color factor and the other was an albino 

 or carried albinism. The matings produced 252 colored young; and 

 if these are added to tables 44 and 45, the grand total of 297 colored 

 young shows quite conclusively that the color factor of the wild C. 

 rufescens, the hybrids, and the tame guinea-pig is epistatic to its absence, 

 irrespectively of the sort of animal which presents the "absence." It 

 is also obvious that some hybrids, in addition to the § wild, must carry 

 the color factors of the wild and of the tame together, but no distinction 

 is visible. Heterozygotes must also occur which received their single 

 dose of the color factor in some cases from the wild, in others from the 

 tame, if we are to believe that the two segregate and keep their identity 

 in the same way that the dark modified agouti factor does. The same 

 reasoning should hold true for black, brown, and extension, but no 

 visible difference in the case of these factors can be detected any more 

 than in the case of the color factor itself. 



HETEROZYGOUS COLORED ANIMALS IN CROSSES WITH ALBINOS. 



A number of matings were made in which female hybrids of various 

 blood-dilutions, from the j wild up through the -^ wild, but hetero- 

 zygous in the color factor, were mated with male albino guinea-pigs. 

 Reciprocal crosses were also made, in which the female hybrids were 

 albinos and the male guinea-pigs were heterozygotes. Matings of this 



