cvalues

C-values, or genome size, refer to the total amount of DNA contained in a haploid genome (1C). It is commonly expressed in picograms of DNA or in base pairs, with 1 picogram roughly equal to 978 megabase pairs. The 2C value denotes the diploid genome content in somatic cells. C-values provide a comparative measure of genome size across species, but they are not a direct measure of gene content or organismal complexity.

A central feature of C-values is the C-value paradox: across diverse taxa, genome size can vary dramatically without a corresponding difference in perceived complexity or number of genes. Some simple organisms or lineages have very large genomes, while other, more complex organisms have much smaller ones. Much of the variation arises from noncoding DNA, including repetitive sequences and transposable elements, as well as differences in ploidy levels.

Measuring C-values typically involves direct DNA quantification methods such as flow cytometry, which compares stained DNA in sampled cells to a standard with a known genome size, or Feulgen densitometry. Sequencing and assembly-based estimates can approximate genome size but may not capture organellar DNA or repeat content accurately. Intra-species and tissue differences can occur due to endoreduplication or varying tissue composition, which may affect measurements.

Significance and limitations: C-values are a foundational metric in comparative genomics, evolution, and ecology, helping researchers study genome evolution, polyploidy, and the contribution of repetitive DNA. However, they do not necessarily reflect gene count, regulatory complexity, or organismal capabilities, and measurements can be influenced by technical and biological factors.