32 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



duced was 102, of which 57 were black and 45 were brown; the most 

 probable expectation would be 51 : 51, but a deviation of 6 individuals 

 is not significant. The black offspring were heterozygous, as was to be 

 expected. This is shown by matings recorded in table 23. The brown 

 offspring were recessive and produced only brown offspring when mated 

 with brown individuals (see table 27). 



Tables 23 and 24 give all the rest of the matings, similar to those of 

 table 22, for the |, yV, and ^V wild females. Both classes of young, 

 black and brown, are expected in about equal numbers from these 

 matings. The actual ratios show both classes produced in proportions 

 which do not deviate farther from equality than similar matings among 

 guinea-pigs. The total numbers were 109 black and 85 brown (table 

 25). There was an excess in favor of the dominant factor, but not of 

 significant size, I believe. 



HETEROZYGOUS BLACKS MATED INTER SE. 



Two matings of this sort were made, which produced 7 black young 

 and 1 brown, the expected ratio being 3 : 1 (see table 26). 



BROWNS MATEDTINTER SE. 



It was stated that brown hybrid | wild offspring were obtained by 

 mating heterozygous blacks with brown males (table 22). Thus a 

 brown race of hybrids was obtained in two generations, by the ap- 

 plication of Mendelian principles, for first homozygous black ^ wild 

 females were mated to brown males, and then their offspring were 

 again mated back to brown, producing brown as well as black offspring. 

 A number of the brown hybrids were used in experiments already 

 described, to prove the dominance of black over brown in these crosses. 

 The rest of the brown hybrids were used in the experiments tabulated in 

 tables 27 and 28; 14 brown | wild females were mated to brown males, 

 producing 78 brown offspring; 13 of the yV wild, and 1 of the ^W wild 

 were similarly mated. The results are clear ; a brown wild hybrid female 

 produces gametes bearing only brown, b. We know that the guinea- 

 pig males do the same. The zygotes, resulting, are bb in formula, i. e., 

 homozygous brown. The summary given in table 29 shows that 111 

 brown offspring resulted from these matings. There was no reversal of 

 dominance, for a wild hybrid breeds true to brown just the same as a 

 guinea-pig. The interesting speculation immediately suggests itself: 

 can we produce a brown race which shall be in all other respects identi- 

 cal with Cavia rufescens? To do so would undoubtedly require a long 

 series of matings, since many independent character differences exist 

 between C. rufescens and C. porcellus. If, however, they all conform 

 with Mendel's law in heredity and the principle of gametic purity 

 holds good in this case, the combination suggested should be capable of 

 realization. 



