Editing GC-content (section)

=== Within-genome variation ===
The GC-ratio within a genome is found to be markedly variable. These variations in GC-ratio within the genomes of more complex organisms result in a mosaic-like formation with islet regions called [[Isochore (genetics)|isochores]].<ref>{{cite journal |author=Bernardi G |title=Isochores and the evolutionary genomics of vertebrates |journal=Gene |volume=241 |issue=1 |pages=3–17 |date=January 2000 |pmid=10607893 |doi=10.1016/S0378-1119(99)00485-0}}</ref> This results in the variations in staining intensity in [[chromosomes]].<ref>{{cite journal |vauthors=Furey TS, Haussler D |title=Integration of the cytogenetic map with the draft human genome sequence |journal=Hum. Mol. Genet. |volume=12 |issue=9 |pages=1037–44 |date=May 2003 |pmid=12700172 |url=http://hmg.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=12700172 |doi=10.1093/hmg/ddg113|doi-access=free }}</ref> GC-rich isochores typically include many protein-coding genes within them, and thus determination of GC-ratios of these specific regions contributes to [[gene mapping|mapping]] gene-rich regions of the genome.<ref>{{cite journal |vauthors=Sumner AT, de la Torre J, Stuppia L |title=The distribution of genes on chromosomes: a cytological approach |journal=J. Mol. Evol. |volume=37 |issue=2 |pages=117–22 |date=August 1993 |pmid=8411200 |doi=10.1007/BF02407346 |bibcode=1993JMolE..37..117S |s2cid=24677431 }}</ref><ref>{{cite journal |vauthors=Aïssani B, Bernardi G |title=CpG islands, genes and isochores in the genomes of vertebrates |journal=Gene |volume=106 |issue=2 |pages=185–95 |date=October 1991 |pmid=1937049 |doi=10.1016/0378-1119(91)90198-K }}</ref>