Editing Human genome (section)

=== Protein-coding genes ===

Protein-coding sequences represent the most widely studied and best understood component of the human genome. These sequences ultimately lead to the production of all human [[protein]]s, although several biological processes (e.g. [[V(D)J recombination|DNA rearrangements]] and [[alternative splicing|alternative pre-mRNA splicing]]) can lead to the production of many more unique proteins than the number of protein-coding genes. 

The human reference genome contains somewhere between 19,000 and 20,000 protein-coding genes.<ref name="Genome">{{cite web |title=Gene |url=https://www.genome.gov/genetics-glossary/Gene#:~:text=And%20genes%20are%20the%20part,of%20the%20entire%20human%20genome. |website=www.genome.gov |access-date=7 January 2025 |language=en}}</ref><ref name = Amaraletal2023 >{{cite journal | vauthors = Amaral P, Carbonell-Sala S, De La Vega FM, Faial T, Frankish A, Gingeras T, Guigo R, Harrow JL, Hatzigeorgiou AG, and Johnson R  | date = 2023 | title = The status of the human gene catalogue | journal = Nature | volume = 622 | issue = 7981 | pages = 41–47 | doi = 10.1038/s41586-023-06490-x | pmid = 37794265 | pmc = 10575709 | arxiv = 2303.13996 | bibcode = 2023Natur.622...41A }}</ref> These genes contain an average of 10 introns and the average size of an intron is about 6 kb (6,000 bp).<ref name="Piovesanetal2019"/> This means that the average size of a protein-coding gene is about 62 kb and these genes take up about 40% of the genome.<ref>{{cite journal | vauthors = Francis WR, Wörheide G | title = Similar Ratios of Introns to Intergenic Sequence across Animal Genomes | journal = Genome Biology and Evolution | volume = 9 | issue = 6 | pages = 1582–1598 | date = June 2017 | pmid = 28633296 | pmc = 5534336 | doi = 10.1093/gbe/evx103 }}</ref>

Exon sequences consist of coding DNA and untranslated regions (UTRs) at either end of the mature mRNA. The total amount of coding DNA is about 1-2% of the genome.<ref name = Hatje_et_al_2019>{{cite journal | vauthors = Hatje K, Mühlhausen S, Simm D, Killmar M | title =  The Protein-Coding Human Genome: Annotating High-Hanging Fruits. | year = 2019 | journal = BioEssays | volume = 41 | issue = 11 | pages = 1900066 | doi = 10.1002/bies.201900066| pmid = 31544971 }}</ref><ref name= Piovesanetal2019>{{cite journal | vauthors = Piovesan A, Antonaros F, Vitale L, Strippoli P, Pelleri MC, Caracausi M | title = Human protein-coding genes and gene feature statistics in 2019 | year = 2019 | journal = BMC Research Notes | volume =12 | issue = 1 | pages = 315 | doi = 10.1186/s13104-019-4343-8| doi-access = free | pmid = 31164174 | pmc = 6549324 }}</ref>

Many people divide the genome into coding and non-coding DNA based on the idea that coding DNA is the most important functional component of the genome. About 98-99% of the human genome is non-coding DNA.