GENETICS 



IN 



RELATION TO AGRICULTURE 



PART I-FUNDAMENTALS 



CHAPTER I 

 THE METHODS AND SCOPE OF GENETICS 



Soon after Mendel's report of investigations in heredity had been 

 rediscovered, it became evident to most biological investigators that a 

 flood of light had been thrown upon the problem of heredity, and the 

 related subjects of variation, development, and evolution. The need 

 for a new term, therefore, to designate this interrelated portion of bio- 

 logical science led Bateson to coin the word, genetics, from the Greek 

 root, FEN, "become." The derivation does not indicate, it must be 

 admitted, very clearly the portion of biology to which the term genetics 

 applies, but this vagueness has in it an element of desirability, for it is 

 extremely difficult to define accurately the boundaries which delimit the 

 province of genetics. Bateson himself has stated that genetics deals with 

 the physiology of heredity and variation; and a favorite statement of 

 authors has been that genetics is the science of the origin of individuals. 

 But these statements they can hardly be called definitions must be 

 qualified carefully in order that they may be understood. Accordingly 

 it has seemed desirable to construct a definition of genetics in purely 

 objective terms. The following definition is, therefore, proposed to ful- 

 fill this need; it, too, will require some qualification: 



Genetics is the science which seeks to account for the resemblances 

 and the differences which are exhibited among organisms related by 

 descent. 



The Content of Genetics. If genetics be defined in the above manner, 

 it may be stated roughly that variation is that portion of genetics 

 having to do with the differences beween organisms, whereas heredity has 

 to do with the resemblances which they exhibit. But this statement 

 does not define very accurately the exact meanings of the two terms; to 

 do this it is necessary to consider certain fundamental facts. 



Organisms exhibit various degrees of difference and resemblance, and 

 classification is made possible first, by resemblances between individuals 

 and, second, by differences between groups of individuals. Further, the 

 orderly interrelations which are exhibited by living beings in general has 



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