CHAPTER XVI 



PRACTICAL APPLICATION OF MENDELIAN PRINCIPLES. 



Meaning of Pttre-bred — Rogueing — Raising iVoveliies — 

 A Practical Example — Unfixable Types — Technical 

 Methods — Sociological Application. 



No one who is acquainted with Mendelian method will 

 doubt that by its use practical breeders of animals and 

 plants may benefit. In so far as they are concerned with 

 the fixation of desirable varieties, or with the creation of new 

 types by re-combination of pre-existing characters, their 

 operations may now be greatly accelerated. 



* ' Pnre-bred " and * ' Cross-bred. 



II But apart from these obvious advantages which it may 



confer, the new^ knowledge of heredity will react most 

 profoundly on the art and practice of the breeder by 

 introducing a new standard of precision. We at length 

 understand the physiological meaning of "pure-bred" and 

 "cross-bred." We know that these ideas must be applied 

 to the several characters of the animal or the plant, rather 

 than to the individual as a whole. For the individual to 

 be altogether pure-bred it must be homozygous in all 

 respects. In current parlance, dogs, for example, derived 

 from a cross a few generations back have been spoken of 

 as "I Bulldog, or -]^ Pointer blood, and so forth. Such 

 expressions are quite uncritical, for they neglect the fact 

 that the characters may be transmitted separately, and that 

 an animal may have only -z]-^ of the " blood " of some pro- 

 genitor, and yet be pure in one or more of his traits. 



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