Editing Genome (section)

== Genome size ==
[[File:Genome_size_vs_protein_count.svg|thumbnail|[[Log–log plot]] of the total number of annotated proteins in genomes submitted to [[GenBank]] as a function of genome size]]
[[Genome size]] is the total number of the DNA base pairs in one copy of a [[haploid]] genome. Genome size varies widely across species. Invertebrates have small genomes, this is also correlated to a small number of transposable elements. Fish and Amphibians have intermediate-size genomes, and birds have relatively small genomes but it has been suggested that birds lost a substantial portion of their genomes during the phase of transition to flight.&nbsp; Before this loss, DNA methylation allows the adequate expansion of the genome.<ref name=":0a" />

In humans, the nuclear genome comprises approximately 3.1 billion nucleotides of DNA, divided into 24 linear molecules, the shortest 45 000 000 nucleotides in length and the longest 248 000 000 nucleotides, each contained in a different chromosome.<ref name="human-T2T">{{cite journal |title=The complete sequence of a human genome |journal=Science |date=2022-03-31 |volume=376 |pages=44–53 |doi=10.1126/science.abj6987 |pmid=35357919|last1=Nurk |first1=Sergey |last2=Koren |first2=Sergey |last3=Rhie |first3=Arang |last4=Rautiainen |first4=Mikko |last5=Bzikadze |first5=Andrey V. |last6=Mikheenko |first6=Alla |last7=Vollger |first7=Mitchell R. |last8=Altemose |first8=Nicolas |last9=Uralsky |first9=Lev |last10=Gershman |first10=Ariel |last11=Aganezov |first11=Sergey |last12=Hoyt |first12=Savannah J. |last13=Diekhans |first13=Mark |last14=Logsdon |first14=Glennis A. |last15=Alonge |first15=Michael |last16=Antonarakis |first16=Stylianos E. |last17=Borchers |first17=Matthew |last18=Bouffard |first18=Gerard G. |last19=Brooks |first19=Shelise Y. |last20=Caldas |first20=Gina V. |last21=Chen |first21=Nae-Chyun |last22=Cheng |first22=Haoyu |last23=Chin |first23=Chen-Shan |last24=Chow |first24=William |last25=De Lima |first25=Leonardo G. |last26=Dishuck |first26=Philip C. |last27=Durbin |first27=Richard |last28=Dvorkina |first28=Tatiana |last29=Fiddes |first29=Ian T. |last30=Formenti |first30=Giulio |issue=6588 |pmc=9186530 |bibcode=2022Sci...376...44N |s2cid=235233625 |url=https://eprints.iisc.ac.in/71762/1/Sci_376-6588_44-531_2022%20.pdf |archive-url=https://web.archive.org/web/20220526104204/https://eprints.iisc.ac.in/71762/1/Sci_376-6588_44-531_2022%20.pdf |archive-date=2022-05-26 |url-status=live |display-authors=1 }}</ref> There is no clear and consistent correlation between morphological complexity and genome size in either [[bacterial genome size|prokaryotes]] or lower [[eukaryotes]].<ref name="Lewin 2004" /><ref>{{cite journal |vauthors = Gregory TR, Nicol JA, Tamm H, Kullman B, Kullman K, Leitch IJ, Murray BG, Kapraun DF, Greilhuber J, Bennett MD |title = Eukaryotic genome size databases |journal = Nucleic Acids Research |volume = 35 |issue = Database issue |pages = D332–38 |date = January 2007 |pmid = 17090588 |pmc = 1669731 |doi = 10.1093/nar/gkl828 }}</ref> Genome size is largely a function of the expansion and contraction of repetitive DNA elements.

Since genomes are very complex, one research strategy is to reduce the number of genes in a genome to the bare minimum and still have the organism in question survive. There is experimental work being done on minimal genomes for single cell organisms as well as minimal genomes for multi-cellular organisms (see [[developmental biology]]). The work is both ''[[in vivo]]'' and ''[[in silico]]''.<ref>{{cite journal |vauthors = Glass JI, Assad-Garcia N, Alperovich N, Yooseph S, Lewis MR, Maruf M, Hutchison CA, Smith HO, Venter JC |title = Essential genes of a minimal bacterium |journal = Proceedings of the National Academy of Sciences of the United States of America |volume = 103 |issue = 2 |pages = 425–30 |date = January 2006 |pmid = 16407165 |pmc = 1324956 |doi = 10.1073/pnas.0510013103 |bibcode = 2006PNAS..103..425G |doi-access = free }}
</ref><ref>{{cite journal |vauthors = Forster AC, Church GM |title = Towards synthesis of a minimal cell |journal = Molecular Systems Biology |volume = 2 |issue = 1 |pages = 45 |date = 2006 |pmid = 16924266 |pmc = 1681520 |doi = 10.1038/msb4100090 }}</ref>

=== Genome size differences due to transposable elements ===
[[File:Genome sizes.png|thumb|Comparison among genome sizes]]

There are many enormous differences in size in genomes, specially mentioned before in the multicellular eukaryotic genomes. Much of this is due to the differing abundances of transposable elements, which evolve by creating new copies of themselves in the chromosomes.<ref name=":0a"/> Eukaryote genomes often contain many thousands of copies of these elements, most of which have acquired mutations that make them defective.