96 



IMll i;ll ANCE IN GUINEA-PIGS. 



TH£ INHERITANCE OF THE AGOUTI OF CAVIA RUFESCENS. 



The writer ha- had the opportunity of experimenting with the hybrid 

 nil : stock developed by Dr. Detlefsen. As the mode of inherit- 



; the fcype of agouti is of special interest in being a character in 

 which two wild species differ, it seemed worth while to obtain additional 

 data. New crosses were made to test out the hypothesis of triple 

 allelomorphs as thoroughly as possible. It may be said at once that 

 the result- obtained completely confirm Detlefsen's hypothesis. 



\\ hen received by the writer, there were only 2 light-bellied agouti 

 hybrid- in the stock which had derived their agouti from C. rufescens. 

 These were A606 and A450, \ and f blood hybrids, respectively. They 

 were crossed with black guinea-pigs and one litter was obtained from 

 li 2 bl.uks from A606 and 1 light-bellied agouti and 1 black from 

 A.450. This light-bellied agouti son unfortunately proved to be sterile, 

 so that experiments with light-bellied rufescens agouti came to an end. 

 Only one light-bellied agouti — born dead — has appeared since then which 

 nied to derive its agouti from C. rufescens, and in this case the 

 parentage was doubtful. Thus in the following experiments, rufescens 

 agouti and ticked-bellied agouti are practically equivalent. It must 

 be emphasized that this was not the case in Detlefsen's experiments, 



that the following results are simpler than those which he encoun- 

 tered in the earlier generations. 



Let us consider first the relations of rufescens agouti and guinea-pig 

 non-agouti. Cross 1 gives matings of non-agoutis with ticked-bellies 

 known to be heterozygous because of a non-agouti parent (table 42). 



Table 42. 



The single agouti light-belly was the son of A450, mentioned above, 

 which, though agouti light-belly, is included under agouti ticked-belly 

 ae a rufescens agouti. The cross shows that ticked-belly is a simple 

 dominant over non-agouti. The ratio of agouti ticked-belly to non- 

 agouti is sufficiently close to a 1 to 1 ratio. If ticked-bellied agouti were 

 due to independent modifying factors or to the residual heredity of 

 rw, acting with the same agouti factor as found in C. cutleri 

 and < . porceUus, non-agouti guinea-pigs should possess factors tending 



