Editing Race and genetics (section)

==Sources of human genetic variation==
{{Main|Human genetic variation}}Genetic variation arises from [[mutations]], from natural selection, migration between populations ([[gene flow]]) and from the reshuffling of genes through [[sexual reproduction]].<ref>{{Cite journal|last=Livingstone|first=Frank|date=Summer 1962|title=On the Non-Existence of Human Races|url=https://moodle.lse.ac.uk/pluginfile.php/618047/mod_resource/content/0/Livingstone%201962.pdf|journal=Chicago Journals|access-date=2019-04-29|archive-date=2021-05-25|archive-url=https://web.archive.org/web/20210525023934/https://moodle.lse.ac.uk/pluginfile.php/618047/mod_resource/content/0/Livingstone%201962.pdf|url-status=dead}}</ref> Mutations lead to a change in the DNA structure, as the order of the bases are rearranged. Resultantly, different polypeptide proteins are coded. Some mutations may be positive and can help the individual survive more effectively in their environment. Mutation is counteracted by [[natural selection]] and by [[genetic drift]]; note too the [[founder effect]], when a small number of initial founders establish a population which hence starts with a correspondingly small degree of genetic variation.<ref>{{Citation|last=Honnay|first=O.|title=Genetic Drift|date=2013 |encyclopedia=Brenner's Encyclopedia of Genetics|pages=251–253|publisher=Elsevier|language=en|doi=10.1016/b978-0-12-374984-0.00616-1 |isbn=978-0-08-096156-9}}</ref> [[Epigenetic inheritance]] involves [[Heredity|heritable]] changes in [[phenotype]] (appearance) or [[gene expression]] caused by mechanisms other than changes in the DNA sequence.<ref>{{Cite journal|last1=Martin|first1=Cyrus|last2=Zhang|first2=Yi|date=June 2007|title=Mechanisms of epigenetic inheritance |journal=Current Opinion in Cell Biology|language=en|volume=19|issue=3|pages=266–272|doi=10.1016/j.ceb.2007.04.002|pmid=17466502}}</ref>

Human phenotypes are highly [[polygenic]] (dependent on interaction by many genes) and are influenced by environment as well as by genetics.

[[Nucleotide diversity]] is based on single mutations, [[single nucleotide polymorphisms]] (SNPs). The nucleotide diversity between humans is about 0.1 percent (one difference per one thousand [[nucleotide]]s between two humans chosen at random). This amounts to approximately three million SNPs (since the human genome has about three billion nucleotides). There are an estimated ten million SNPs in the human population.<ref name="Jorde2004">{{cite journal |last1=Jorde |first1=Lynn B |last2=Wooding |first2=Stephen P |author1-link=Lynn Jorde |title=Genetic variation, classification and 'race' |journal=[[Nature Genetics]] |date=November 2004 |volume=36 |issue=11 |series=Supplemental |pages=28–33 |doi=10.1038/ng1435 |pmid=15508000 |url=https://www.nature.com/articles/ng1435 |access-date=27 June 2024 |publisher=[[Nature Portfolio]] |issn=1546-1718 |oclc=8091998144 |s2cid=1500915 |id=Jorde2004 |archive-url=http://web.archive.org/web/20240622010650/https://www.nature.com/articles/ng1435 |archive-date=22 June 2024}}</ref>

Research has shown that non-SNP ([[structural variation|structural]]) variation accounts for more human genetic variation than single nucleotide diversity. Structural variation includes [[copy-number variation]] and results from [[Deletion (genetics)|deletions]], [[Chromosomal inversion|inversions]], [[Genetic insertion|insertions]] and [[Gene duplication|duplications]]. It is estimated that approximately 0.4 to 0.6 percent of the genomes of unrelated people differ.<ref name='Tishkoff&Kidd2004'/><ref name="kGP15">{{cite journal|display-authors=6|vauthors=Auton A, Brooks LD, Durbin RM, Garrison EP, Kang HM, Korbel JO, Marchini JL, McCarthy S, McVean GA, Abecasis GR|date=October 2015|title=A global reference for human genetic variation|journal=Nature|volume=526|issue=7571|pages=68–74|bibcode=2015Natur.526...68T|doi=10.1038/nature15393|pmc=4750478|pmid=26432245}}</ref>