The mating and breeding of poultry . of their ownkind without the slightest bad effect. It is easy to accountfor the supposed observed cases of contamination by theaccidental mating, without the breeders knowledge, of thehen with another male than the one with which she issupposed to be mated. Mendelism.—In the preceding sections, we have at-tempted to present the leading principles of breeding as theyhave been brought out by practical experience. It should beadded that a great deal has been discovered in recent yearsabout the laws of heredity, which underlie these practicalprinciples. It^woul
The mating and breeding of poultry . of their ownkind without the slightest bad effect. It is easy to accountfor the supposed observed cases of contamination by theaccidental mating, without the breeders knowledge, of thehen with another male than the one with which she issupposed to be mated. Mendelism.—In the preceding sections, we have at-tempted to present the leading principles of breeding as theyhave been brought out by practical experience. It should beadded that a great deal has been discovered in recent yearsabout the laws of heredity, which underlie these practicalprinciples. It^would, however, go beyond the scope of thisbook to go into the subject in detail. There are a number ofbooks on the subject which may be recommended to thosewho are interested. The following may be mentioned:Genetics in Relation to Agriculture, by E. B. Babcock and R. E. Clausen, and Eugenics, by W. E. Castle, of Mendelian Heredity, by Morgan, Sturtevant, Muller and Bridges, 1915. PRINCIPLES OF BREEDING 13. 14 THE MATING AND BREEDING OF POULTRY According to earlier views, heredity was looked upon asfluid in nature. We still use such expressions as half blood,quarter blood, etc., which convey this idea. It now appears,however, that the hereditary material is composed of unitswhich are handed on almost indefinitely without behavior may be compared better to that of little solidscontained in the germ cell than to fluids. The variations inmost characteristics, it is true, depend on so many of theseunits that the mode of inheritance after crossing may stillbe compared roughly to the blending of fluids. A compari-son of the hereditary basis of a characteristic to a pile ofshot is better, however, when it comes to explaining theeffects of inbreeding, the nature of prepotency, etc. A few characteristics depend on such a small number ofunits that the effects of the different ones are easily followedin crosses. Mendels law of heredity was originall
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