SUPPLEMENT II 



THE RELATION OF GENETICS TO 

 PHYSIOLOGY AND MEDICINE 



NOBEL LECTURE, PRESENTED IN STOCKHOLM ON JUNE 4, 1934 

 By Dr. THOMAS HUNT MORGAN 



DIRECTOR OF THE Wll. G. KERCKHOFF LABORATORIES, CALIFORNIA INSTITUTE OF TECHNOLOGY 



The study of heredity, now called 

 genetics, has undergone such an ex- 

 traordinary development in the present 

 century, both in theory and in practice, 

 that it is not possible in a short address 

 to review even briefly all its outstanding 

 achievements. At most I can do no more 

 than take up a few topics for discussion. 



Since the group of men with whom I 

 have worked for twenty years has been 

 interested for the most part in the chro- 

 mosome-mechanism of heredity, I shall 

 first briefly describe the relation between 

 the facts of heredity and the theory of 

 the gene. Then I should like to discuss 

 one of the physiological problems im- 

 plied in the theory of the gene; and 

 finally, I hope to say a few words about 

 the applications of genetics to medicine. 



The modern theory of genetics dates 

 from the opening years of the present 

 century, with the discovery of Mendel's 

 long-lost paper that had been overlooked 

 for thirty-five years. The data obtained 

 by de Vries in Holland, Correns in Ger- 

 many and Tschermak in Austria showed 

 that Mendel's laws are not confined to 

 garden peas, but apply to other plants. 

 A year or two later the work of Bateson 

 and Punnett in England and Cuenot in 

 France made it evident that the same 

 laws apply to animals. 



In 1902 a young student, William 

 Sutton, working in the laboratory of 

 E. B. Wilson, pointed out clearly and 

 completely that the known behavior of 

 the chromosomes at the time of matura- 

 tion of the germ-cells furnishes us with 

 a mechanism that accounts for the kind 

 of separation of the hereditary units 

 postulated in Mendel's theory. 



The discovery of a mechanism, that 

 suffices to explain both the first and the 

 second law of Mendel, has had far-reach- 

 ing consequences for genetic theory, espe- 

 cially in relation to the discovery of addi- 

 tional laws ; because the recognition of a 

 mechanism that can be seen and followed 

 demands that any extension of Mendel's 

 theories must conform to such a recog- 

 nized mechanism ; and also because the 

 apparent exceptions to Mendel's laws, 

 that came to light before long, might, in 

 the absence of a known mechanism, have 

 called forth purely fictitious modifica- 

 tions of Mendel's laws or even seemed to 

 invalidate their generality. We now 

 know that some of these "exceptions" 

 are due to newly discovered and demon- 

 strable properties of the chromosome 

 mechanism, and others to recognizable 

 irregularities in the machine. 



Mendel knew of no processes taking 

 place in the formation of pollen and egg- 



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