OLD TYPES AND NEW 



it requires more than a single generation to establish 

 a homozygous dominant strain. 



In random inbreeding of diverse strains if the re- 



A 



(cessives are constantly eliminated as they appear, a 

 /population is gradually obtained which is composed 

 \ of an increasing number of dominants so that after 

 only a few generations the chances are much reduced 

 that recessives will again appear, which means the prac- 

 tical purity of the strain. 



E. GENOTYPIC SELECTION 



/" The success, however, of any method of originating 

 \ new types of organisms or of improving old ones must 

 / depend in the long run upon the selection of germinal 



differences. 



j The difficulty here of course lies in the fact, that we 

 may only know the potential germplasm from its per- 

 formance in producing somatoplasm, but Mendelism 

 with its analysis of the genes through breeding^ cer- 

 tainly has gone a long way toward making genotypic 

 selection possible and definite. Moreover, the preserva- 

 tion and exploitation of mutations when they are known 

 is certainly along the line of genotypic selection, since 

 mutations when isolated may become the progenitors of 

 desirable new lines. Accordingly until the secret of 

 the origin of mutations is solved the work of the suc- 

 cessful breeder consists to a very large extent in simply 

 taking what mutations nature spontaneously furnishes 

 to him rather than in attempting to force nature into 

 producing something new. 



