Fig. 6.1. Gregor Mendel. (A portrait 

 by Flatter from Journal of Heredity, 

 1940, vol. 31, reprinted by permission.) 



This method of experimental breeding under controlled conditions that give 

 the best environment for the organisms makes it possible to know in detail 

 the character of heredity and variation in any particular individual, as well 

 as to compare specifically individuals of successive generations. In order to 

 interpret fully the result of experimental breeding it becomes necessary to 

 study, by the method of cytology, the germ cells from which new individuals 

 arise. The greatest progress in the theory of genetics has come from correla- 

 tion of the results obtained from experimental breeding and such study of 

 germ cells. A fourth way of approaching the problem of the mechanism of 

 heredity and variation is the method of experimental embryology, in which 

 individuals of known ancestry are subjected to conditions that are not usual 

 for their development. Comparison of results obtained from these several 

 methods of approach has yielded considerable information concerning many 

 facts of heredity and variation and has led to the formulation of theories 

 of the mechanism involved. Clarification and extension of our knowledge of 

 genetics may be expected to continue in view of the great amount of interest 

 in research in this field. 



The Method of Biometry 



Investigators who use the biometrical method collect a great amount of 

 observational data upon organisms under natural conditions, analyze these 

 data by statistical methods, and formulate generalizations concerning heredity 

 and variation that will be true for the whole group but for no particular 

 individual. Sir Francis Gallon (1822-1911) did the first serious biometrical 

 work when he studied the relation between the height of parents and the 

 height of offspring in over a thousand human families. The original study of 



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