CHAPTER XIX 

 THE PRACTICAL VALUE OF GENETICS 



The human race was successful to a remarkable extent in shaping 

 other organisms to its needs and desires before the advent of 

 science. Many of our domestic animals and plants were developed 

 without the shghtest knowledge of the underlying principles of 

 heredity and breeders even now continue to apply the practical 

 principles of their craft without such knowledge. As in so many 

 other fields of human activity, theory in this field is not essential 

 to practical success. 



The science of genetics has shown us not only how the results 

 of the past have been obtained but also why many desired results 

 have never been secured. By clearly establishing the fundamental 

 principles of inheritance it has shown what we can hope to do in 

 the future, how it can best be accomplished and in some cases 

 how human efforts in this field are hedged about by apparently 

 insurmountable barriers. Some things known to practical breeders 

 and scientists alike can only be determined by experiment, but 

 in general the best results can be obtained only through the com- 

 bination of scientific knowledge with sound practical methods. 

 As in all fields, limited knowledge of any kind cannot hope to 

 compete with broad knowledge of all phases of the subject. 



The methods of plant and animal breeding are dependent upon 

 the two general methods, hybridization and selection. In a work 

 of this kind it is impossible to mention the details of method 

 involved; discussion must be limited to these fundamental proc- 

 esses, some of their results and their common limitations. 



Hybridization. This process, as the beha\dour of Mendelian 

 unit characters shows, makes it possible to secure combinations of 

 characters found in nature only separately in different species or 

 strains. The combination desired may easily be secured if the 

 difference between the parents is slight, or it may involve a 

 multitude of difficulties if the parents belong to different species. 

 As a general rule any combination is possible, even though it 

 may not be practicable to secure it. 



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