CHARACTERS OF DISTINCT PAIRS 95 



A cross between a yellow round and a green 

 wrinkled would have involved the same two pairs 

 of characters. The hybrid would have been, as in 

 the case I have shown, yellow round ; that is to say, 

 exactly like one of its parents. The second hybrid 

 generation would have been the same in the two cases. 

 The difference between the two cases, of course, lies 

 in the distribution of the characters over the parent 

 forms ; in other words, in the case I have figured, 

 each parent has a dominant member of one pair 

 and a recessive member of the other pair. But 

 when a yellow round is crossed with a green wrinkled 

 the former has both the dominant members and the 

 latter both the recessive ones. That is why in this 

 case the result of the cross is identical with one of the 

 parents. I have, however, described a cross between 

 two individuals, each of which bears a dominant 

 and each a recessive character, for a definite reason, 

 to illustrate the fact that the dominance or recessive- 

 ness of a character is not a result of constitutional 

 vigour or weakness of the animal or plant that bears 

 it, but is a property peculiar to that particular 

 character. A cross between a round and a wrinkled 

 does not show this ; nor does a cross between a 

 yellow and a green ; nor even does a cross between a 

 yellow round and a green wrinkled. In all these 

 cases the hybrid is like one of its parents, and we 

 have no means of knowing that its character is not 

 determined by the superior vigour of that parent. 

 But directly we have seen the result of a cross between 

 two forms, each of which possesses a dominant 



