6o 



COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 



Evidently there is a strong 1 tendency for white, when it dominates in 

 a first cross, to behave as a dominant also among the progeny of that 

 cross ; and likewise for yellow, when it dominates in a first cross, to 

 behave as a dominant among the progeny of that cross. This indicates 

 clearly the persistence from generation to generation of relative poten- 

 cies of gametes of a particular sort. As regards the relative proportions 

 of white and of yellow cocooned young, it is noteworthy that there is 

 throughout the experiment a slight excess of yellows over the expected, 

 indicating a somewhat superior potency of that character, which, in 

 matings between other white-cocooned and yellow-cocoonecl races, was 

 found to be uniformly dominant. 



That cross-breeding may modify the relative potencies of gametes 

 seems highly probable, yet the evidence for this idea at present avail- 

 able is inconclusive. It consists principally in an observed excess of 

 partial-rough young over the expected proportion in certain matings, 

 which will presently be described, but the numbers of young as yet 

 produced in these experiments are too small to be at all conclusive. 



One mating of pure rough animals (R. cT 2002 X R. 9 2003) pro- 

 duced, as expected, only rough young, five in number (see p. 63). 



Hybrid rough animals, R. (Sm.), when mated with pure rough 

 animals, have produced, as expected, only rough young, 57 being fully 

 rough (Condition A, p. 57) and i partial-rough (Condition B or C). 



The one partial-rough animal occurred in a litter of three young borne 

 by R. 9 2040 mated with hybrid R. (Sm.) c? 994. This female had 

 previously borne two fully rough young by Sm. cT 2060 (see p. 58). 

 It is probable, therefore, that the hybrid c? 994 did form some smooth 

 gametes of unusual potency, though, unfortunately, he was not tested by 

 other matings with rough females. 



Hybrid rough animals, R. (Sm.) in character, when mated with 

 smooth ones, have produced 127 rough young and 146 smooth ones, 

 equality of the two classes being expected on the Mendelian hypothesis 

 of segregation. Of the 127 rough young, all except 6 have Condition 

 A, the fully rough coat. The 6 partial-rough young were produced in 

 four different litters, each by a different pair. They were as follows : 



