Greilhuber et al.[1] have suggested some new layers of terminology and associated abbreviations to clarify this issue, but these somewhat complex additions are yet to be used by other authors.
Even among authors who have attempted to trace the origin of the term, there had been some confusion because Hewson Swift did not define it explicitly when he coined it in 1950.
[2] In his original paper, Swift appeared to use the designation "1C value", "2C value", etc., in reference to "classes" of DNA content (e.g., Gregory 2001,[3] 2002[4]); however, Swift explained in personal correspondence to Prof. Michael D. Bennett in 1975 that "I am afraid the letter C stood for nothing more glamorous than 'constant', i.e., the amount of DNA that was characteristic of a particular genotype" (quoted in Bennett and Leitch 2005[5]).
[5][7] Protist genomes have been reported to vary more than 300,000-fold in size, but the high end of this range (Amoeba) has been called into question.
However, although there is no longer any paradoxical aspect to the discrepancy between C-value and gene number, this term remains in common usage.
Some prefer the term C-value enigma because it explicitly includes all of the questions that will need to be answered if a complete understanding of genome size evolution is to be achieved (Gregory 2005).
Moreover, the term paradox implies a lack of understanding of one of the most basic features of eukaryotic genomes: namely that they are composed primarily of non-coding DNA.
Some have claimed that the term paradox also has the unfortunate tendency to lead authors to seek simple one-dimensional solutions to what is, in actuality, a multi-faceted puzzle.
However, it was soon found that C-values (genome sizes) vary enormously among species and that this bears no relationship to the presumed number of genes (as reflected by the complexity of the organism).
In general terms, the C-value enigma relates to the issue of variation in the amount of non-coding DNA found within the genomes of different eukaryotes.
The C-value enigma, unlike the older C-value paradox, is explicitly defined as a series of independent but equally important component questions, including: †Source of table: Doležel et al., 2003[12] The formulas for converting the number of nucleotide pairs (or base pairs) to picograms of DNA and vice versa are:[12] By using the data in Table 1, relative masses of nucleotide pairs can be calculated as follows: A/T = 615.383 and G/C = 616.3711, bearing in mind that formation of one phosphodiester linkage involves a loss of one H2O molecule.