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, 1t 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, TEN, “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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