CHAPTER 17 

 GENETICS 



"Like begets like" is a familiar phrase whose origin undoubtedly 

 traces back to the dim beginnings of human civilization. Our heritage 

 of domesticated plants and animals is a tribute to the early recognition 

 of this principle by our unknown ancestors. 



First it is recognized that the young of any species is of the same 

 type as its parents, that is, dogs have puppies, cats have kittens, corn 

 produces corn. This fact naturally is of significance, but of even more 

 importance is the fact that within species, varieties can also be relied 

 upon to reproduce themselves. The many breeds of dogs are well known 

 and have been developed into pure breeding stock; these same facts are 

 evident among plants. At first wild plants and animals must have been 

 domesticated through the empirical selection of desirable traits. In this 

 way early man was able to make the transition from dependence upon 

 vagaries of hunting to the more certain production of food by his do- 

 mesticated animals and plants. 



This original development of desirable races of plants and animals 

 was done without benefit of any knowledge of the physical basis of 

 the inheritance. It remained for a long series of scientists to discover the 

 processes of sexuality, gametogenesis, and the physical basis of in- 

 heritance. With the development of this knowledge, plant and animal 

 breeding has taken great forward strides. The present-day descendants 

 of the early domestic animals and plants would scarcely be recognized 

 by the first early breeders. Through this knowledge, the food supply 

 of the world has to a great extent kept pace with the ever-increasing 

 world population. 



These same principles can be observed among human beings. 

 The resemblance of children to parents is constantly the subject of 

 great discussion among families. While this resemblance is often very 

 obvious, differences do exist. While the child resembles his parents, he 



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