CROSSES OF CAVIA CUTLERI. 



17 



the F 2 results, omitting only albinos (which have been dealt with 

 already). When this is done we get the results shown in table 10. 

 No class deviates from expectation enough to suggest "linkage" or 

 " coherence" of characters involved in the cross. 



Table 10. 



(e) INTENSITY AND DILUTION AMONG THE HYBRIDS. 



It has been stated that the Fi young produced by the cross of female 

 albinos of race B with male cutleri were dark golden agouti in color, 

 much darker than the cutleri parent. This darkening of the color per- 

 sisted undiminished into the following generation (F 2 ). Of the 58 

 colored Fi young derived from this cross none was as light in coloration 

 as the cutleri grandparent. Hence it would appear that the darker 

 coloration introduced by the cross, apparently through the albino 

 parent, does not behave as a simple Mendelian character either domi- 

 nant or recessive; otherwise pale-colored F 2 young should have been 

 produced. Whatever factors, Mendelian or otherwise, are responsible 

 for the darkening of the pigmentation are evidently unconnected with 

 the so-called color factor, since they are transmitted by albinos, which 

 lack this factor. 



A very different result was observed in crosses of the same cutleri 

 males with females of race C. The colored animals of race C are very 

 pale cream-colored. The F t young which they produced showed a 

 more intense yellow than either parent, but were much lighter than the 

 hybrids produced in the cross with race B albinos. (See plate 3.) 



Among their F 2 young appeared some very light-colored individuals, 

 16 being recorded in a total of 56 young produced by pairs which pro- 

 duced no albinos. The pale-colored young were not confined to any 

 one colored class, but were recorded among the agoutis, blacks, cinna- 

 mons, and yellows. (See table 11.) The proportion recorded is close 

 to one-fourth, from which it would seem that dilution had been intro- 

 duced as a recessive character by the cream guinea-pig grandparents. 

 Since, however, C. cutleri is relatively pale in pigmentation, it is prob- 

 able that some of the animals classified as pale were not "dilute," owing 

 to a factor derived from the guinea-pig ancestor, but because of condi- 

 tions derived from the cutleri ancestor. This statement applies to the 

 young of matings which produced albinos as well as to those which did 

 not. The significant thing is that more pale-pigmented young and 

 those which excelled in paleness were obtained from those matings 

 which did not involve albinsim. 



