Developmental Genetics 



269 



SUMMARY AND CONCLUSIONS 



Phenogenetics, the study of how genetically determined phenotypes come into being, can 

 be investigated for morphological traits. In this case, phenogenetics starts out as a study 

 of the developmental genetics of morphology. Such studies reveal that the final morpho- 

 logical outcome, which is usually a pleiotropic one, is based upon earlier morphological 

 changes which are in turn preceded by physiological changes occurring still earlier in develop- 

 ment. The developmental genetics of morphological features thus becomes explicable in 

 terms of gene-caused physiological changes, or by means of the study of physiological 

 genetics. 



The latter studies reveal that the physiological effect of the genotype is sometimes intra- 

 cellular and sometimes intercellular. The action certain cells have on cells located elsewhere 

 may involve a general or localized control of growth rates and differentiation. This action 

 may occur nearby, via induction, or it may take place at a distance, by means of a general 

 nutritive effect, or by hormones (or nerve impulse or muscular contraction). It is also 

 found that the reacting tissue may have its competence to respond to these influences changed 

 for genetic reasons. 



Comprehension of physiological genetics must, in turn, involve an understanding of how 

 genes influence metabolism, and since metabolism involves the study of physical and chemical 

 reactions, phenogenetics must ultimately be described in biophysical and biochemical terms. 

 You may recall, from Chapter 10, that this was the path taken (morphology to physiology 

 to biochemistry) in the phenogenetic study of the gene for sickle cell anemia. 



REFERENCES 



Beutler, E., Yeh, M., and Fairbanks, V. F., "The Normal Human Female as a Mosaic of 

 X-Chromosome Activity; Studies Using the Gene for G-6-PD-Deficiency as a 

 Marker," Proc. Nat. Acad. Sci., U.S., 48:9-16, 1962. 



Gluecksohn-Waelsch, 

 1951. 



S., "Physiological Genetics of the Mouse," Adv. in Genet., 4:2-49, 



Goldschmidt, R. B., Theoretical Ge- 

 netics, Berkeley, University of 

 California Press, 1955. 



Hadorn, E., Developmental Genetics 

 and Lethal Factors, New York, 

 John Wiley & Sons, 1961. 



Landauer, W., "On the Chemical Pro- 

 duction of Developmental Ab- 

 normalities," J. Cell Comp. 

 Physiol., 43 (Suppl.):261-305, 

 1954. 



Waddington, C. H., Organizers and 

 Genes, Cambridge University 

 Press, 1947. 



Wright, S., "The Physiology of the 

 Gene," Physiol. Rev., 41:487- 

 527, 1941. 



Richard Benedict Goldschmidt 

 (1878-1958). (By permission of Ge- 

 netics, Inc., vol. 45, p. 1, 1960.) 



