Chapter 8 



Genetics: The Heritable Transmission of Catalysts 



The Nobel prize in medicine for 1935 was awarded to Thomas 

 Hunt Morgan, the outstanding geneticist, who with his able 

 collaborators, Calvin B. Bridges, A. H. Sturtevant and others, 

 did so much to establish experimentally the view that hereditary 

 characters are carried by particulate units called genes (or gens),* 

 arranged linearly in the chromosomes of the germ cells. This 

 award to Morgan called attention to the great importance of 

 developments in the science of genetics, a branch of biology deal- 

 ing with heredity and its mechanisms. 



While breeders of cattle, horses, dogs, pigs, fowl and other do- 

 mestic animals, as well as farmers and seedsmen dealing with vege- 

 tables, wheat and other grains, had from time out of mind been 

 making selections of favored forms, it was Gregor Mendel, Abbot 

 of Briinn (Bohemia) who introduced atomism into genetics, as 

 J. B. S. Haldane puts it. In his cloister garden, Mendel assembled 

 the results of breeding experiments with the common garden pea 

 (Pisum sativum), which were published in 1865, only six years 

 after the appearance of Charles Darwin's "Origin of Species." 

 Mendel attributed the differences, which he found were distrib- 

 uted by heredity, to discrete representative factors or producers, 

 which in general pass unaltered through successive generations, 

 though their distribution may vary. It was not until 1900, eight- 

 een years after Mendel's death, that the importance of his work 

 was independently recognized by three distinguished botanists, 

 Hugo de Vries (Holland), C. Correns (Germany) and G. Tscher- 

 mak (Austria). 



Mendel crossed a tall with a dwarf pea, and observed how these 

 characters were inherited. All members of the first family (F x ) 

 were tall; but this was not the case with the second family (F 2 ) 

 developing from the seeds of the F x hybrids. 



* The Standard Dictionary of 1913 gives timidly the following definition of "gen": 

 "A minute hypothetical particle supposed to be the bearer of hereditary qualities." 



154 



