BIOCHEMICAL STUDIES OF HYBRIDS 303 



To conclude references to zoological investigations of hybrids, 

 Fox et al. (1961) studied the toad species, Bufo fowleri, B. valliceps, 

 and their natural hybrids by means of starch-gel electrophoresis and 

 found distinctive differences in the parental species (the actual par- 

 ents of the hybrids were not available). The hybrids contained all 

 components of both parents without any new "hybrid" substances 

 detected. It is evident that two levels of biochemical categories are 

 affected in hybridization. In serological studies one may be measuring 

 substances in the general category of enzymes. Equally affected, how- 

 ever, as a result of hybridization will be the products of these enzymes, 

 which may in many cases be small molecular weight basic metabolites, 

 or secondary products. So, in hybrids, all types of substances may be 

 affected in such a way as to increase over-all biochemical complexity. 

 In backcrosses, furthermore, it would not be predicted that any bio- 

 chemical system simpler than that of either parent would appear 

 under normal circumstances. This generahzation apphes to secondary 

 substances as well as proteins and is valid except when the original 

 parents are complex heterozygotes. It may not necessarily be applied 

 to secondary substances in considering an F2 population. 



Many biochemical studies other than those involving serology 

 in nature have been conducted on hybrids. The specific substances 

 investigated are non-protein and usually fall into the general category 

 of secondary products of metabolism. The term secondary product 

 refers to compounds not involved either in basic energy transfer 

 processes or in the synthesis of metabolites essential to the life of the 

 individual cell. Complex substances of a lipoid or carbohydrate nature, 

 although they may possibly serve as energy sources, are considered as 

 secondary products. 



The idea of applying biochemical methods to hybrids is an old 

 one. Perhaps the best way to illustrate this point is to use the exact 

 words of one early investigator, Reichert, who, in 1919, published an 

 834 page treatise with the optimistic and visionary title of A Biochemic 

 Basis for the Study of Problems of Taxonomy, Heredity, Evolution, 

 etc., with Especial Reference to the Starches and Tissues of Parent- 

 stocks and Hybrid-stocks and the Starches and Hemoglobins of 

 Varieties, Species, and Genera. Most of this work by Reichert was 

 botanical, although the author was a medical doctor. He used, 

 primarily, starch characters in his hybrid studies. It is perhaps debat- 

 able whether the characters were truly biochemical. For example, 

 some characters such as form, nature of hilum and lamellae, and size 

 were morphological while others, such as iodine and aniline reactions, 

 polariscopic and temperature reactions were more strictly biochemical. 



