14 



INHERITANCE IN GUINEA-PIGS. 



agoutis there are 43, of the blacks 15, and of the albinos 17. The 

 numerical relations of the classes suggest a dihybrid Mendelian ratio 

 of 9:3:4, which is in entire agreement with existing knowledge of 

 color inheritance in guinea-pigs (Castle, 1905; Sollas, 1909). C. cutleri 

 is evidently homozygous for all Mendelian color factors, since it breeds 

 very true to color. Albino guinea-pigs from a black race are known 

 to possess two independent recessive modifications from this condition, 

 lacking both the agouti factor and the so-called color factor. As 

 regards these factors, then, the wild race, cutleri, forms gametes AC, the 

 albino forms gametes ac, and the F! hybrids form gametes of the four 

 types AC, Ac, aC, and ac. From recombination of such gametes 

 should arise in F 2 zygotes as in table 5. 



TABLE 5. 



1 AACC 



2 AaCC 

 2 AACc 

 4 AaCc 



9 agouti 



1 aaCC 



2 aaCc 



3 black 



1 AAcc 



2 Aacc 



3 albino 



1 albino 



The several kinds of albinos being similar in appearance, the expected 

 result is 9 agouti, 3 black, 4 albino. The agreement with this expecta- 

 tion is fairly close (see table 6). 



TABLE 6. 



(b) CROSS 9 ALBINO (RACE C) X <? CUTLERI. 



FI animals from the cross between an albino of race C and a cutleri 

 male have produced 44 F 2 young, which fall into 7 color classes, dis- 

 regarding differences of intensity of pigmentation. These classes and 

 their numerical representation among the 44 young are as follows: 

 golden agouti, 10; black, 1; cinnamon, 8; black-eyed cream, 4; brown- 

 eyed cream, 3; chocolate, 4; albino, 14. (See plate 4.) The occurrence 

 of these several classes of F 2 young is what previously existing knowl- 

 edge of color inheritance among guinea-pigs would have led us to expect, 

 for it was known that albinos of race C differed from agoutis in the same 

 two factors as the albinos of race B, viz, the agouti factor and the color 

 factor. In addition, the albinos of race C were known to differ from 

 agoutis in two other factors, seen respectively in chocolate and yellow 

 races. The chocolate race may be considered to have arisen by a 

 recessive modification of the black factor B, and the yellow race by a 

 similar modification of the extension factor E. Accordingly this cross 



