ENTITIES REPRESENTING CHARACTERS 127 



If a character is represented by chromosomes or any 

 other entities perhaps smaller than chromosomes, then it 

 is necessary to assume not only that the character which 

 appears is represented, but also some latent characters. 

 For instance, a child may be exceedingly like some ancestor 

 several generations removed, although the likeness has not 

 appeared between whiles. Again, in the disease haemophilia 

 (bleeding) a generation is generally skipped, for this disease 

 very rarely appears in females, although it is transmitted 

 through the females. 1 A man who is a " bleeder " may 

 have sons and daughters none of whom have his disease. 

 It will, however, very probably appear in his grandchildren 

 by his daughters, but not in his grandchildren by his sons. 

 Thus the disease is latent in the females, patent in the 

 males, although transmitted almost always through the 

 females and not through the males. 



If a character were represented hi one chromosome only, 

 it would very likely be eliminated in one or two generations. 

 We find, however, that individual characters often continue 

 for several generations. It is probable, therefore, if char- 

 acters are represented by entities, that there will be several 

 entities representing differences in the same character. We 

 will take ten as a convenient hypothetical number, and 

 assume a group of these divergences in the same character 

 which are favourable to the organism and so are subject to 

 selection. We will represent these favourable divergences 

 as A, and suppose that two entities A are present in one 

 parent, and one in the other. All the other entities we 

 will represent as X. In one parent the entities will be 

 2A+8X, in the other parent the entities will be A+9X. 

 In the gametes these entities are halved, and in those of 

 one parent there may be 2A+3X, A+4X, or 5X. In the 

 gametes of the other parent there may be A+4X, or 5X. 

 In the offspring of these parents there may be 3A+7X, or 

 10X, or anything between the two. If the A's give the 

 individual an advantage, those offspring with 3A will succeed 



1 Osier, W., The Principles and Practice of Medicine, 1904. 



