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C-value is the amount, in picograms, of DNA contained within a haploid nucleus (e.g. 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 polyploids the C-value may represent two or more genomes contained within the same nucleus.
The onion test is a way of assessing the validity of an argument for a functional role for junk DNA.It relates to the paradox that would emerge if the majority of eukaryotic non-coding DNA were assumed to be functional and the difficulty of reconciling that assumption with the diversity in genome sizes among species. [1]
The paradox was resolved with the discovery that most of the differences were due to the expansion and contraction of repetitive DNA and not the number of genes. Some researchers speculated that this repetitive DNA was mostly junk DNA. The reasons for the changes in genome size are still being worked out and this problem is called the C-value ...
The case for junk DNA was summarized in a lengthy paper by David Comings in 1972 where he listed four reasons for proposing junk DNA: [28] some organisms have a lot more DNA than they seem to require (C-value paradox), current estimates of the number of genes (in 1972) are much less than the number that can be accommodated,
The C 0 t value is the product of C 0 (the initial concentration of DNA), t (time in seconds), and a constant that depends on the concentration of cations in the buffer. Repetitive DNA will renature at low C 0 t values, while complex and unique DNA sequences will renature at high C 0 t values. The fast renaturation of the repetitive DNA is ...
The following table is a representative sample of Erwin Chargaff's 1952 data, listing the base composition of DNA from various organisms and support both of Chargaff's rules. [14] An organism such as φX174 with significant variation from A/T and G/C equal to one, is indicative of single stranded DNA.
The first approach is GC and AT asymmetry. [2] Jean R. Lobry was the first to report, in 1996, [7] the presence of compositional asymmetry in the genomes of three bacteria: E. coli, Bacillus subtilis, and Haemophilus influenzae.
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