390 Maine: agrtculturai, experiment station. 1912. 



But here 'selection' is simply one part of a system of breeding, 

 which to be successful must be based on a definite knowledge of 

 gametic as well as somatic conditions. It is very, very far re- 

 moved from a blind 'breeding of the best to the best to get the 

 best.' The latter plan alone may, as in the case of fecundity, 

 fail absolutely to bring about any progressive change whatever. 

 It has never yet been demonstrated, so far as I know, that the 

 absolute somatic value of a particular hereditary factor or deter- 

 minant (i.e., its power to cause a quantitatively definite degree 

 •of somatic development of a character) can be changed by se- 

 lection on a somatic basis, however long continued. To deter- 

 mine, by critical experiments which shall exclude beyond doubt 

 ■or question such effects of selection as those noted under i and 2 

 above, whether the absolute somatic value of factors may be 

 ■changed by selection, or in any other way, is one of the funda- 

 mental problems of genetics. 



Prepotency 



One of the least understood phenomena in genetics is that 

 which the practical breeder calls 'prepotency.' When the scien- 

 tific student of genetics deals with the matter at all he is rather 

 apt either to' throw it over entirely as a 'breeder's superstition,' 

 or to take it as something 'given' to help him out of a difficulty 

 in the interpretation of results which fail to conform to expec- 

 tation. Some time a more searching investigation of this phe- 

 nomenon must be made than is implied in either of these lines 

 of procedure. 



In a former paper (27, p. 324), it was suggested that the evi- 

 dence indicated, for certain productive characters at least, that 

 hereditary high performa.nce tended to behave as a Mendeiian 

 dominant to hereditary low performance. The following state- 

 ment was then made : 



*'If this suggestion is true it gives at once, I think, a possible 

 €lue to the explanation of a part at least of the known facts re- 

 garding what is called prepotency in the practical breeding of 

 domestic animals for performance. It is customary in practice 

 to regard an animal as prepotent in breeding for performance 

 when the progeny of that individual uniformily tend to resem- 

 ble it closely in respect tO' the character bred for, regardless of 

 the other parent in each mating. Let it now only be considered 



