504 Orga?jis?ns Are Products of Heredity mid Envirofimejit unit ix 



Fig. 455 H01V itiany buportaiit environmental factors can yon name which Ijave 

 improved these cows on a inoderii dairy jarm? Are the characters due to this good 

 environment inherited':' (walker-gordon laboratories) 



The breeder seeks the best environ- 

 ment. The modern farmer houses his cat- 

 tle in barns that are hght and clean; he 

 knows that sunshine is as necessary to his 

 animals as to himself. He feeds them sci- 

 entifically and inoculates them against 

 disease. Thus his cattle grow to a larger 

 size and produce more milk. He raises his 

 crops in fields that have been carefully 

 tilled and he fights the insects and fungi 

 that attack his plants. By such methods 

 the yield per acre of wheat, corn, and of 

 other food plants can be much increased. 

 In a good environment animals and 

 plants are given an opportunity to grow 

 big and strong. If the breeder has plants 

 with desirable mutations or good gene 

 combinations they are able thus to thrive. 

 But the characteristics dependent on the 

 environment arc acquired characters. 

 They are not passed on to the offspring. 



While a good environment does not pro- 

 duce new types it is a factor which must 

 not be neglected. 



The work of plant and animal breeders. 

 Every breeder, besides giving his plants 

 and animals the best possible environ- 

 ment, decides on what he wants and then 

 proceeds along one of three lines to get 

 new and better varieties. He can select 

 the most desirable form in each genera- 

 tion. Careful selection and breeding pro- 

 duce varieties with a better gene combi- 

 nation than had been present before. This 

 is a gradual and slow method of improv- 

 ing animals and plants. The breeder is 

 also alert to detect new desirable charac- 

 ters caused by mutations or other chro- 

 mosomal changes. These can be used for 

 establishing new varieties but they occur 

 rarely. And, lastly, through hybridiza- 

 tion he can sometimes bring together in 



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