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PRINCIPLES OF POULTRY BREEDING 



ferent character. Variation is rather the result of changes taking 

 place in existing characters, due to the changing relation between 

 characters. 



The fact that individuals do vary makes improvement possible 

 through selection and breeding which would otherwise be impos- 

 sible. Indeed, without this factor there would be no chance for 

 either improvement or deterioration; the type would be fixed in 

 all its characteristics. 



Variations are of two kinds, those which increase the useful- 

 ness of the individual and those which are undesirable or create 



FIG. 120. Barred Plymouth Rock chicks from the same mating and of the same age, 

 showing morphological variation. 



an inferior condition. It is the duty and purpose of the breeder 

 to select and intensify desirable variations whenever possible. 



Types of Variation. The unit of variability is not the individ- 

 ual, but the breed. The real measure of variation is the breed 

 character. Four distinct types of variation have been described 

 by Davenport.* The following brief discussion shows practical 

 examples of these forms in poultry breeding and gives a clearer 

 conception of variations. These types are (1) morphological, 

 (2) substantive, (3) meristic, and (4) functional. 



Morphological variation has to do with differences in form or 



*" Principles of Breeding," by Eugene Davenport. 



