C-value: Difference between revisions

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== 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.<ref name="Bennett2005"/><ref name="Gregory2005">{{cite book |author=Gregory T.R. |year=2005 |chapter=Genome size evolution in animals |title=The Evolution of the Genome |editor=T.R. Gregory |pages=3–87 |publisher=Elsevier |___location=San Diego|title-link=The Evolution of the Genome }}</ref> [[Protist]] genomes have been reported to vary more than 300,000-fold in size, but the high end of this range ([[Amoeba (genus)|''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; for example, some single-celled [[protozoa|protists]] have genomes much larger than that of [[humans]]. This observation was deemed counterintuitive before the discovery of [[non-codingRepeated sequence (DNA)|repetitive DNA]]. It became known as the C-value paradox as a result. However, although there is no longer any [[paradox]]ical 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, or [[extinction]] risk (for recent reviews, see Bennett and Leitch 2005;<ref name="Bennett2005"/> Gregory 2005<ref name="Gregory2005"/>).

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]].