THE characteristics by which organisms are recognized are the expressions of the information contained in their nucleic acids. As such, a knowledge of their DNA base composition, or if possible the base sequences of some organisms, should be a valuable asset in their classification. Lee, Wahl and Barbu1were the first to recognize the taxonomic importance of analysing the average DNA base compositions of micro-organisms. While the overall base compositions of some unrelated organisms may be the same, this equivalence would appear to be a minimum requirement for extensive base sequence homologies2and genetic compatibility (except in certain cases of F-duction3). Thus, similar DNA base compositions in two organisms might indicate close relationships whereas dissimilar base compositions would indicate that the organisms are unrelated.
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