COAT CHARACTERS IN GUINEA PIGS AND RABBITS. 6l 



The smooth animals used in these matings were all pure-bred except 

 9 1338, which had a hybrid, R. (Sm.), father, but a pure-bred smooth 

 mother. We can not assume, however, that these hybrid rough ani- 

 mals formed in general weak rough gametes, for R. (Sm.) c? mi had 

 in all, by smooth females, 13 rough offspring, but only in the mating 

 with 9 644 was a partial-rough individual produced ; again R. (Sm.) 

 c? 1 178 had rough offspring (6 in all) by three different smooth females, 

 but only in the mating with 9 1661 did he produce a partial-rough 

 animal. It would seem that the degree in which dominance is realized 

 in the zygote is dependent upon the relative potency of the gametes 

 uniting, and that potency is apt to be more variable in the gametes of 

 cross-bred than in that of'pure-bred animals. If so, hybrid rough ani- 

 mals bred inter se, or with cross-bred rough or smooth individuals, 

 should produce an especially large proportion of partial-rough young. 

 The experiments made are as yet hardly extensive enough to give a 

 decisive answer to this question. 



Fully rough hybrid, R, (Sm.), animals bred inter se, have produced 

 in all 32 rough young, only one of which is a partial-rough. This one 

 was produced by the following mating : 



R. (Sm.) cT mi X R' (Sin.) 9 1438, produced i /?., i PR., 2 Sm. 



This same male, it will be remembered, produced a partial-rough indi- 

 vidual by the smooth female 644. 



We may return now to the question whether the condition of unusual 

 potency in the smooth gametes of animals producing partial-rough 

 young is handed on to the posterity of those animals. If the partial- 

 rough character of hybrid animals is due simply to imperfectly realized 

 dominance of the character borne by the dominant gamete, and if the 

 characters united in the zygote maintain their distinctness and segre- 

 gate with the same relative potencies, when gametes are formed by 

 the hybrid as they possessed before, then we should expect to get fully 

 rough, as well as partial-rough offspring, by mating partial-rough 

 animals either inter se or with rough animals. The result of mating 

 partial-rough with smooth animals would depend upon the relative 

 potency of the gametes formed by the smooth mates ; if none of their 

 gametes were unusually potent, then the offspring should be half fully 

 rough and half smooth, without partial-rough young. But if half 

 the gametes formed by the smooth animals are unusually potent, then 

 the offspring should be visibly as i JR. to i PR. to 2 Sm. 



