Editing Evolution (section)

== Heredity ==
{{further|Introduction to genetics|Genetics|Heredity}}
[[File:ADN static.png|thumb|left|[[DNA]] structure. [[nucleobase|Bases]] are in the centre, surrounded by phosphate–sugar chains in a [[double helix]].]]

Evolution in organisms occurs through changes in heritable characteristics—the inherited characteristics of an organism. In humans, for example, [[eye colour]] is an inherited characteristic and an individual might inherit the "brown-eye trait" from one of their parents.<ref>{{cite journal |last1=Sturm |first1=Richard A. |last2=Frudakis |first2=Tony N. |date=August 2004 |title=Eye colour: portals into pigmentation genes and ancestry |journal=[[Trends in Genetics]] |volume=20 |issue=8 |pages=327–332 |doi=10.1016/j.tig.2004.06.010 |issn=0168-9525 |pmid=15262401}}</ref> Inherited traits are controlled by genes and the complete set of genes within an organism's [[genome]] (genetic material) is called its ''[[genotype]]''.<ref name="Pearson-2006">{{cite journal |last=Pearson |first=Helen |date=25 May 2006 |title=Genetics: What is a gene? |journal=Nature |volume=441 |issue=7092 |pages=398–401 |bibcode=2006Natur.441..398P |doi=10.1038/441398a |issn=0028-0836 |pmid=16724031 |s2cid=4420674 |doi-access=free}}</ref>

The complete set of observable traits that make up the structure and behaviour of an organism is called its ''[[phenotype]]''. Some of these traits come from the interaction of its genotype with the environment while others are neutral.<ref>{{cite journal |last1=Visscher |first1=Peter M. |last2=Hill |first2=William G. |author-link2=William G. Hill |last3=Wray |first3=Naomi R. |author-link3=Naomi Wray |date=April 2008 |title=Heritability in the genomics era — concepts and misconceptions |journal=Nature Reviews Genetics |volume=9 |issue=4 |pages=255–266 |doi=10.1038/nrg2322 |issn=1471-0056 |pmid=18319743 |s2cid=690431}}</ref> Some observable characteristics are not inherited. For example, [[suntanned]] skin comes from the interaction between a person's genotype and sunlight; thus, suntans are not passed on to people's children. The phenotype is the ability of the skin to tan when exposed to sunlight. However, some people tan more easily than others, due to differences in genotypic variation; a striking example are people with the inherited trait of [[albinism]], who do not tan at all and are very sensitive to [[sunburn]].<ref>{{cite journal |last1=Oetting |first1=William S. |last2=Brilliant |first2=Murray H. |last3=King |first3=Richard A. |date=August 1996 |title=The clinical spectrum of albinism in humans |journal=[[Molecular Medicine Today]] |volume=2 |issue=8 |pages=330–335 |doi=10.1016/1357-4310(96)81798-9 |issn=1357-4310 |pmid=8796918}}</ref>

Heritable characteristics are passed from one generation to the next via [[DNA]], a [[molecule]] that encodes genetic information.<ref name="Pearson-2006" /> DNA is a long [[biopolymer]] composed of four types of bases. The sequence of bases along a particular DNA molecule specifies the genetic information, in a manner similar to a sequence of letters spelling out a sentence. Before a cell divides, the DNA is copied, so that each of the resulting two cells will inherit the DNA sequence. Portions of a DNA molecule that specify a single functional unit are called genes; different genes have different sequences of bases. Within cells, each long strand of DNA is called a [[chromosome]]. The specific location of a DNA sequence within a chromosome is known as a [[locus (genetics)|locus]]. If the DNA sequence at a locus varies between individuals, the different forms of this sequence are called alleles. DNA sequences can change through mutations, producing new alleles. If a mutation occurs within a gene, the new allele may affect the trait that the gene controls, altering the phenotype of the organism.<ref name="Futuyma_2005">{{harvnb|Futuyma|2005}}{{page needed|date=December 2014}}</ref> However, while this simple correspondence between an allele and a trait works in some cases, most traits are influenced by multiple genes in a [[quantitative trait loci|quantitative]] or [[epistatic]] manner.<ref>{{cite journal |last=Phillips |first=Patrick C. |date=November 2008 |title=Epistasis—the essential role of gene interactions in the structure and evolution of genetic systems |journal=Nature Reviews Genetics |volume=9 |issue=11 |pages=855–867 |doi=10.1038/nrg2452 |issn=1471-0056 |pmc=2689140 |pmid=18852697}}</ref><ref name="Min Lin-2006">{{cite journal |author1=Rongling Wu |author2=Min Lin |date=March 2006 |title=Functional mapping — how to map and study the genetic architecture of dynamic complex traits |journal=Nature Reviews Genetics |volume=7 |issue=3 |pages=229–237 |doi=10.1038/nrg1804 |issn=1471-0056 |pmid=16485021 |s2cid=24301815}}</ref>