This paper is a study of the genetic material derivable from the simplest (and among the oldest) life forms, principally bacteria. Many definitions from microbiology are developed and interrelated, and procedures for the study of DNA from simple organisms are described. The history of the elucidation of the microbiological significance of prokaryotic DNA, an early and persistent building block of life on earth, is revisited from many perspectives.
A genome consists of "all the genetic material in a cell" (8 :204). A prokaryote is an "organism that lacks a membrane-bound nucleus" (8:216); although some argue that there is much more to a prokaryote than that, and rather more subtle differences from eukaryotes than the latter having a membrane-bound nucleus (18:2-3). Heritage et al. give a six-page comparison (8:2-7).
DNA, centrally, is a nucleic acid (deoxyribonucleic acid, hence DNA), whose function along with other nucleic acids is to "store, maintain, and transmit genetic information" (16:103). Very fundamentally, should DNA and its sister nucleic acids not be able, for any reason, to pass along an organism's existing traits during reproduction or division, the existing organism must either change (mutate or evolve) or die, and possibly both. Otherwise, the offspring would be the same as the parents in all demonstrable characteristics. Among the possibilities of change, of course, is the possibility that prokaryotic organisms have changed, changed again, and changed back or at least changed to a familiar, look-alike, almost-former state.
Postgate gives a fascinating description of this "genetic fluidity" among the three-billion-year-old bacteria, and he describes how trillions of bacterial generations, and specifically their genetic material, have affected other organisms' lives and bodies, including the genetic material of eukaryotes such as people (10:258-9). Moreover, he is fairly certain that sufficient evol...