C-value 2354482 221241723 2008-06-23T17:54:10Z DOI bot 6652755 Citation maintenance. Initiated by [[User:Fconaway|Fconaway]]. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. The term '''C-value''' refers to the amount of [[DNA]] contained within a [[haploid]] [[Cell nucleus|nucleus]] (e.g., in a gamete or one half the amount in a [[diploid]] [[somatic cell]]) of a [[eukaryotic]] organism. In some cases (notably among diploid organisms), the terms C-value and [[genome size]] are used interchangeably, however in [[Polyploidy|polyploids]] the C-value may represent two genomes contained within the same nucleus. Greilhuber et al. (2005) have suggested some new layers of terminology and associated abbreviations to clarify this issue, but these somewhat complex additions have yet to be used by other authors. C-values are reported in [[picogram]]s. == Origin of the term == 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. 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, 2002); 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). 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]]). 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 == C-values vary enormously among species. In animals they range more than 3,300-fold, and in land plants they differ by a factor of about 1,000 (Bennett and Leitch 2005; Gregory 2005). [[Protist]] genomes have been reported to vary more than 300,000-fold in size, but the high end of this range ([[Amoeba|''Amoeba'']]) has been called into question. Variation in C-values bears no relationship to the complexity of the organism or the number of [[genes]] contained in its genome, an observation that was deemed wholly counterintuitive before the discovery of [[non-coding DNA]] and which became known as the [[C-value paradox]] as a result. However, although there is no longer any [[Paradox|paradoxical]] aspect to the discrepancy between C-value and gene number, this term remains in common usage. For reasons of conceptual clarification, the various puzzles that remain with regard to genome size variation instead have been suggested to more accurately comprise a complex but clearly defined puzzle known as the C-value enigma. C-values correlate with a range of features at the [[Cell (biology)|cell]] and organism levels, including cell size, [[cell division]] rate, and, depending on the [[taxon]], body size, [[metabolic rate]], developmental rate, [[Organ (anatomy)|organ]] complexity, geographical distribution, and/or [[extinction]] risk (for recent reviews, see Bennett and Leitch 2005; Gregory 2005). ==Calculating C-values== <div> {| class="wikitable" |+Table 1: Relative Molecular Weights of Nucleotides† |- !Nucleotide !Chemical formula !Relative [[molecular weight]] |- |2′-deoxyadenosine 5′-monophosphate || C<sub>10</sub>H<sub>14</sub>N<sub>5</sub>O<sub>6</sub>P ||align="right"|331.2213 |- |2′-deoxythymidine 5′-monophosphate || C<sub>10</sub>H<sub>15</sub>N<sub>2</sub>O<sub>8</sub>P ||align="right"|322.2079 |- |2′-deoxyguanosine 5′-monophosphate || C<sub>10</sub>H<sub>14</sub>N<sub>5</sub>O<sub>7</sub>P ||align="right"|347.2207 |- |2′-deoxycytidine 5′-monophosphate || C<sub>9</sub>H<sub>14</sub>N<sub>3</sub>O<sub>7</sub>P ||align="right"|307.1966 |} †Source of table: Doležel ''et al.'', 2003<ref name="Dolezel2003">{{cite journal |author=Doležel J, Bartoš J,Voglmayr H, Greilhuber J |title=Letter to the editor: Nuclear DNA Content and Genome Size of Trout and Human |journal=Cytometry |volume=51A |issue=2 |pages=127–128 |year=2003 |doi=10.1002/cyto.a.10013}}</ref> </div> By using the data in Table 1, relative weights of nucleotide pairs can be calculated as follows: AT = 615.3830 and GC = 616.3711. Provided the ratio of AT to GC pairs is 1:1, the mean relative weight of one nucleotide pair is 615.8771 (±1%).<ref name="Dolezel2003"/> The relative molecular weight may be converted to an absolute value by multiplying it by the [[atomic mass unit]] (1 u), which equals one-twelfth of a mass of 12C, i.e., 1.660539 × 10<sup>-27</sup> kg. Consequently, the mean weight of one nucleotide pair would be 1.023 × 10<sup>-9</sup> [[picogram|pg]], and 1 pg of DNA would represent 0.978 × 10<sup>9</sup> base pairs.<ref name="Dolezel2003"/> The formulas for converting the number of nucleotide pairs (or base pairs) to picograms of DNA and vice-versa are:<ref name="Dolezel2003"/> genome size (bp) = (0.978 x 10<sup>9</sup>) x DNA content (pg) DNA content (pg) = genome size (bp) / (0.978 x 10<sup>9</sup>) 1 pg = 978 Mb The current estimates for human female and male diploid genome sizes are 6.406 × 10<sup>9</sup> bp and 6.294 × 10<sup>9</sup> bp, respectively.<ref name="IHGSC2001">{{cite journal |title=International Human Genome Sequencing Consortium. Initial sequencing and analysis of the human genome |journal=Nature |volume=409 |pages=860–921 |year=2001}}</ref> By using the conversion formulas given above, diploid human female and male nuclei in G<sub>1</sub> phase of the [[cell cycle]] should contain 6.550 and 6.436 pg of DNA, respectively. == References == {{reflist}} *Bennett, M.D. and I.J. Leitch. 2005. Genome size evolution in plants. In ''[[The Evolution of the Genome]]'' (ed. T.R. Gregory), pp. 89-162. Elsevier, San Diego. *Gregory, T.R. 2001. Coincidence, coevolution, or causation? DNA content, cell size, and the C-value enigma. ''Biological Reviews'' 76: 65-101. *Gregory, T.R. 2002. A bird's-eye view of the C-value enigma: genome size, cell size, and metabolic rate in the class Aves. ''Evolution'' 56: 121-130. *Gregory, T.R. 2005. Genome size evolution in animals. In ''[[The Evolution of the Genome]]'' (ed. T.R. Gregory), pp. 3-87. Elsevier, San Diego. *Greilhuber, J., J. Dolezel, M. Lysak, and M.D. Bennett. 2005. The origin, evolution and proposed stabilization of the terms 'genome size' and 'C-value' to describe nuclear DNA contents. ''Annals of Botany'' 95: 255-260. *Swift, H. 1950. The constancy of deoxyribose nucleic acid in plant nuclei. ''Proceedings of the National Academy of Sciences of the USA'' 36: 643-654. *Vendrely, R. and C. Vendrely. 1948. La teneur du noyau cellulaire en acide désoxyribonucléique à travers les organes, les individus et les espèces animales&nbsp;: Techniques et premiers résultats. ''Experientia'' 4: 434-436. == See also == * [[Animal Genome Size Database]] * [[Cell nucleus]] * [[Comparative genomics]] * [[C-value enigma]] * [[C-value paradox]] * [[Genome]] * [[Genome size]] * [[Human genome]] * [[Junk DNA]] * [[Noncoding DNA]] * [[Plant DNA C-values Database]] * [[Selfish DNA]] * [[Transposable elements]] == External links == *[http://www.genomesize.com Animal Genome Size Database] *[http://www.rbgkew.org.uk/cval/homepage.html Plant DNA C-values Database] *[http://www.zbi.ee/fungal-genomesize/index.php Fungal Genome Size Database] [[Category:DNA]] [[it:C-value]] [[zh:C值]]