PRACTICAL IMPORTANCE OF MENDEL'S LAW 373 



Of great interest is De Vries's evidence that certain mutations, 

 involving Mendelian unit -characters, are associated with chromo~ 

 some-changes. In his " Mutation Factor in Evolution " (1915) 

 Ruggles Gates shows in circumstantial detail that peculiarities 

 marking the various mutants of the Evening Primrose (CEnothera) 

 are correlated with observable alterations in the organisation of 

 the fertilised egg-cell, especially as regards the chromosomes. In his 

 " Mechanism of Mendelian Heredity " (1915) T. H. Morgan shows, 

 for instance, that a particular unit-character in the fruit-fly (Droso- 

 phila) is almost certainly correlated with a change in a definitely 

 localised area of a single chronosome. 



6. Practical Importance oj Mendel's Discovery 



As Mendel's discovery is extended it is bound to have a great 

 influence on the breeding of animals and the cultivation of 

 plants. Wherever it is applicable it will afford a solid basis 

 for action, enabling the breeder to reach his desired result more 

 surely, more rapidly, and more economically. The case we have 

 mentioned of the varieties of wheat susceptible and immune 

 to " rust " is in itself very suggestive. 



A case like that of the Andalusian fowls shows how immediate 

 may be the practical utility of Mendelism. The pairing of blue 

 Andalusians yields only six blues to the dozen; the crossing 

 of a black and a white yields twelve blues to the dozen. 



The impossibility of fixing the blue Andalusian characters 

 into a stable race is simply due to the fact that the blue 

 Andalusians are hybrids, and the same is probably true of cases 

 like the sugar-beet, where selection seems to have ceased to 

 produce further improvement. 



The breeder who wishes to get a stable and pure strain rapidly, 

 has obviously a clue in the behaviour of the extracted recessives 

 and the extracted dominants of the F 2 generation. There are 

 many similar practical applications of Mendelian results. 



Inbreeding. Breeders who have with carefulness evolved a 

 fine herd are often very loath to introduce fresh blood, even 

 when they suspect that they are approaching the limits of safe 

 inbreeding. But ij Mendelism applies to the organisms bred, 

 then it does not seem as if the introduction of fresh blood need 

 affect the purity of the stock. A cross is effected to secure 



