250 APPLICATION OF BREEDING PRINCIPLES 



new blood of the same breed. It is usually done with two objects 

 in view: (1) To correct some defect which it is apparently impos- 

 sible to correct within the line which has been establishe/i and fol- 

 lowed; or (2) to introduce some desirable feature which the estab- 

 lished line does not possess. 



If careful selection has been made in line breeding, it is doubt- 

 ful if out-crossing should be resorted to except for one of the above- 

 mentioned reasons. Even under these conditions, out-crossing 

 should be cautiously done, lest the variations which are produced 

 follow a different line or direction from that which is desired. 



Reciprocal Crosses. By reciprocal crossing is meant the alter- 

 nate crossing of male and female of two different breeds or varieties. 

 The behavior of reciprocal crosses in poultry breeding is an inter- 

 esting phenomenon. When two races of the same general type 

 and character are crossed, the progeny are similar, no matter which 

 type was used as the male parent. If, however, the parents are 

 widely different, the resulting progeny will vary with the varying 

 size of the parents. For example, if one parent is a bantam and 

 the other a large bird, the size of the egg, and therefore of the 

 chick, will be like that of the mother. If the mother is a bantam 

 the chicks will be small; if the mother is of full size the chicks also 

 will be full size. There are many minor features which give similar 

 results, but generally the progeny resemble each other regardless 

 of parent alternations. 



Control of Sex. A problem concerning which there is much 

 speculation and discussion is the possibility of controlling sex. 

 From the standpoint of economy and profit, it would be a great 

 advantage in poultry breeding to have a large majority of the 

 progeny females, since one male is sufficient for a considerable 

 number of hens, and the female is the real economic producing 

 unit. Despite the fact that numerous rules have been formulated 

 for controlling this factor, our present knowledge of the laws of 

 reproduction does not permit us to expect any great variation in 

 either direction from the usual 50 per cent of each sex. Sex is 

 undoubtedly determined, in birds at least, at the time of fertiliza- 

 tion by the union of certain kinds of germ cells, and its control is 

 at present beyond human power. The sex of the egg after being 

 laid is not known. 



Summary of Breeding Systems. Considerable has been said 

 concerning different systems of breeding. The choice of a method 

 should be governed entirely by the purpose to be accomplished. 



