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== Origin of the Term - C-value==
Many authors have incorrectly assumed that the 'C' in "C-value" refers to "characteristic", "content", or "complement". 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.<ref name="Swift1950">{{cite journal |author=Swift H |year=1950 |title=The constancy of deoxyribose nucleic acid in plant nuclei |journal=Proceedings of the National Academy of Sciences of the USA |volume=36 |issue=11 |pages=643–654|pmid=14808154 |pmc=1063260 |doi=10.1073/pnas.36.11.643|bibcode=1950PNAS...36..643S |doi-access=free }}</ref> 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,<ref name="Gregory2001">{{cite journal |author=Gregory TR |year=2001 |title=Coincidence, coevolution, or causation? DNA content, cell size, and the C-value enigma |journal=Biological Reviews |volume=76 | doi = 10.1017/S1464793100005595 | pmid=11325054 |issue=1 |pages=65–101|doi-broken-date=15 April 2025 }}</ref> 2002<ref name="Gregory2002">{{cite journal |author=Gregory TR |year=2002 |title=A bird's-eye view of the C-value enigma: genome size, cell size, and metabolic rate in the class Aves |journal=Evolution |volume=56 |pmid=11913657 |issue=1 |pages=121–30 |doi=10.1111/j.0014-3820.2002.tb00854.x|doi-access=free }}</ref>); 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<ref name="Bennett2005">{{cite book |vauthors=Bennett MD, Leitch IJ |year=2005 |chapter=Genome size evolution in plants |title=The Evolution of the Genome |editor=T.R. Gregory |pages=89–162 |publisher=Elsevier |___location=San Diego|title-link=The Evolution of the Genome }}</ref>). This is in reference to the report in 1948 by Vendrely and Vendrely of a "remarkable constancy in the nuclear DNA content of all the cells in all the individuals within a given animal species" (translated from the original [[French language|French]]).<ref name="Vendrely1948">{{cite journal |author=Vendrely R, Vendrely C |year=1948 |title=La teneur du noyau cellulaire en acide désoxyribonucléique à travers les organes, les individus et les espèces animales : Techniques et premiers résultats |journal=Experientia |volume=4 |issue=11 |pages=434–436 |language=French|pmid=18098821 |last2=Vendrely |doi=10.1007/bf02144998|s2cid=22272730 }}</ref> Swift's study of this topic related specifically to variation (or lack thereof) among [[chromosome]] sets in different cell types within individuals, but his notation evolved into "C-value" in reference to the haploid DNA content of individual species and retains this usage today.
== Variation among species ==
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The '''{{visible anchor|C-value enigma}}''' or '''{{visible anchor|C-value paradox}}''' is the complex puzzle surrounding the extensive variation in nuclear [[genome size]] among [[eukaryotic]] species. At the center of the C-value enigma is the observation that genome size does not correlate with organismal complexity; for example, some single-celled [[Protozoa|protists]] have genomes much larger than that of [[humans]].
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.<ref name="kew" /> For these reasons, in 2003 the term "C-value enigma" was endorsed in preference to "C-value paradox" at the Second Plant Genome Size Discussion Meeting and Workshop at the [[Royal Botanic Gardens, Kew]], [[United Kingdom|UK]],<ref name=kew>{{Cite web |url=http://www.rbgkew.org.uk/cval/pgsm/index.html
and an increasing number of authors have begun adopting this term.
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