18 



INHERITANCE IN GUINEA-PIGS. 



TABLE 11. Distribution of intensity and dilution among the F% young derived 

 from the cross 9 race CX <? cutleri. 



It was expected that albinos of race C would produce a much larger 

 proportion of pale-colored grandchildren, but strange to say this expec- 

 tation was not realized; 81 F 2 colored young produced in matings 

 which yielded albinos (showing that the guinea-pig characters had been 

 received through albino gametes) included only 11 pale-colored young, 

 and none of these is recorded as being paler in color than the cutleri 

 grandparent. It would appear, therefore, that the albino gametes of 

 race C mothers do not transmit the dilution seen in the cream-colored 

 animals of race C. This would be a puzzling state of affairs had not 

 Wright (1915) already discovered an easy explanation for it, viz, that 

 the dilution of the cream race is an allelomorph of albinism, and so can 

 not be transmitted in the same gamete with albinism. 



Comparing the F 2 hybrids derived from race C crosses with those 

 derived from race B crosses, it is certain that the pigmentation of both 

 is darker than that of wild C. cutleri, but the intensity of the race B 

 hybrids much exceeds that of the race C hybrids. Among the race B 

 hybrids no evidence can be discovered of segregating Mendelian inten- 

 sity factors; among the race C hybrids dilution segregates as a simple 

 Mendelian recessive, precisely as does albinism, but apparently no 

 gamete transmits both dilution and albinism, for the reason that they 

 are alternative conditions of the same factor. Aside from the factorial 

 difference in dilution, how does race B differ from race C? Apparently 

 in no simple factorial way, but in a general way as regards energy of 

 pigment production, in which hybrids of both races surpass C. cutleri 

 but differ quantitatively from each other. No Mendelian explanation 

 of this difference is at present justified by the observations made. 



(f) SIGNIFICANCE OF THE RESULTS OBSERVED. 



The complete fertility of the hybrids produced by crossing wild Cavia 

 cutleri with the guinea-pig is in striking contrast with the sterility of 

 hybrids between C. rufescens and the guinea-pig, as observed by Det- 



