Heredity - 505 



Table 26-2— Partial List of Heritable Traits in Man, with Probable Genie Relations 



however, is not so much that it proved that 

 nontasting is determined by a single pair of 

 recessive genes, since this could be ascer- 

 tained directly by noting the absence of tast- 

 ers among the offspring of nontaster X non- 

 taster unions. The true importance lies in 

 the validation of the analytical methods used 

 in population genetics — methods that are 

 now being used extensively by many workers. 

 Heritable Defects of Metabolism. In 1908, 

 Archibald Garrod, an English physician of 

 outstanding scientific insight, reported upon 

 a number of "inborn errors of metabolism," 

 which appeared to be caused by heritable 



defects in one or another of the metabolic 

 enzymes of various patients. Subsequently 

 Garrod's viewpoint has been amply substan- 

 tiated. Now, in fact, about a do/en such 

 metabolic defects are recognized. Among 

 these, perhaps the most important are: al- 

 kaptonuria, phenylketonuria, agammaglob- 

 ulinemia, galactosemia, sickle cell anemia, 

 and albinism. In each case the lack of a single 

 enzyme appears to be responsible for the 

 condition, and the inheritance is mediated 

 by a single pair of mutant, or defective, genes, 

 usually of recessive character. Moreover, a 

 study of the inheritance of these metabolic 



