46 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



species cross in the light of this criticism. It is hoped that the foregoing 

 discussion will show that the law of alternative inheritance has obtained 

 consistently through eight generations of hybrids ranging from the 

 intensely wild to the dilute-blooded generations, and in many different 

 kinds of matings. 



The real significance of this alternative inheritance is that a character 

 such as wild agouti, the allelomorph of which has been wild agouti for 

 centuries undoubtedly, can without apparent disturbance take up the 

 non-agouti character as its allelomorph, or the tame-agouti character. 

 The same is true of the other coat characters. Whether this is due to 

 the innate nature of the allelomorphic pairs or due to the material 

 bodies which carry the factors can for the present only be a matter of 

 speculation. 



The general conclusions are: 



1. Cavia rufescens is homozygous in agouti, black, brown, the exten- 

 sion factor, smooth coat, uniformitj^, intensity, and short hair. 



2. Hybrids of any eolor variety can be produced by mating it to the 

 guinea-pig. The color and coat characters of C. rufescens are dominant 

 in every case, except as regards roughness and texture of coat and 

 possibly the agouti factor. 



3. The hybrids have the zygotic color formula which one would 

 expect to obtain by mating a pure agouti strain of guinea-pigs to some 

 other color variety of guinea-pigs. 



4. The agouti of hybrids, though always epistatic to the nonagouti 

 condition of the same, is subject to modification as a result of the cross. 



5. This modified wild agouti is very distinct from the tame agouti, 

 and is recessive to it. The two segregate clearly in the F2 generation. 

 Both are allelomorphic to each other and to their absence. Hybrids 

 were produced homozygous in agouti, yet bearing the wdld and the 

 tame agouti. 



6. Roughness derived from the tame guinea-pig is very imperfectly 

 dominant over the smooth wild coat. This incomplete dominance is 

 lost in later, more dilute, wild-blooded generations, and the rough coat 

 becomes normally dominant. 



7. The uniform coat of the wild is dominant to the spotted coat of 

 the tame. In later generations the hybrids show the incomplete 

 dominance of uniformity over spotting, which is characteristic of the 

 guinea-pig. 



8. Any color variety known in guinea-pigs can be produced in the 

 hybrids. Combinations of tame and wild characters can be made, 

 even bringing in such a morphological character as polydactylism from 

 a tame race, together with the peculiar agouti of the wild race. 



9. The inheritance of coat and color characters throughout this 

 species cross is in accordance with Mendel's law. It is equally true of 

 matings of hybrids inter se, and of matings of hybrids of either sex with 

 guinea-pigs. 



