18 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



classes of young had they been more prohfic. The law of probable 

 error would account for the occasional occurrence of these ratios of : 4 

 and 4 : 0, where we expect equality as an average result. 



It is, therefore, clear that when a wild species of cavy known to be 

 homozygous in agouti is mated with a tame race lacking agouti, and 

 hybrid females are thus produced, these are heterozygous in the agouti 

 factor. 



Let us follow the I wild agouti offspring of the heterozygous ^ wild 

 females. Since they were produced by matings in which only one 

 parent (the ^ wild) carried agouti, they too should be heterozygous; 

 20 females of the 47 agouti I wild individuals were mated to non-agouti 

 guinea-pig males (table 7). Just as in the matings of table 6, each 

 female should in this case produce both agouti and non-agouti young. 

 Females 95, 97, and 98 produced young of only one kind as far as we 

 know, but since the total young of these 3 females is only 4, we may 

 legitimately neglect them. The total number of offspring of all the 

 females in this experiment (table 7) was 55 agouti and 59 non-agouti, 

 a close approximation to the expected equality. 



It is interesting to note that, whereas the ^ wild females gave a slight 

 preponderance of agouti young, the | wild agouti females gave the 

 reverse. Adding the matings of tables 6 and 7, we see that our intense 

 wild-blooded hybrids acted just as the guinea-pig does in matings of 

 this description, and produced an approximate equality of agouti and 

 non-agouti young, in this case 102 agouti to 95 non-agouti. The most 

 probable expectation is either 98 or 99 of either sort. 



We have traced (in tables 8, 9, 10) the matings of all the rest of our 

 heterozygous agouti females with non-agouti males. Since, in the 

 intense wild-blooded hybrids, the color inheritance for agouti has been 

 shown to be the same as that described by Castle (1905) and Sollas 

 (1909) in the guinea-pig, we had no reason to expect our dilute-blooded 

 hybrids to behave differently, for they surely are still more like guinea- 

 pigs than the earlier generations of hybrids. In table 8 are summarized 

 the matings of heterozygous | wild females with recessive guinea-pig 

 males and in the lower division of the table matings reciprocal to those 

 just described. Since the reciprocal matings gave like results they may 

 be combined. The offspring, all told, are 50 agouti and 37 non-agouti. 

 In tables 9 and 10 .are summarized matings in which the females alone 

 bore agouti. They evidently produced gametes of two sorts in equal 

 numbers, those bearing agouti and those without it. 



Tables 6 to 10 deal with similar matings, namely, the heterozygous 

 agouti mated to non-agouti, in the different blood dilutions. The 

 summary of these experiments constitutes table 11. It is noteworthy 

 that some of these agouti hybrids received their agouti character from 

 the original wild parent and some others (after the | wild of table 8) 

 received the agouti from the tame. The two are distinguishable. 



