Editing Heredity (section)

==Overview==
[[File:Jug Ear Heredity.jpg|thumb|right|150px|Heredity of phenotypic traits: a father and son with [[prominent ear]]s and crowns.]]
[[File:DNA animation.gif|thumb|500px|[[DNA]] structure. [[nucleobase|Bases]] are in the centre, surrounded by phosphate–sugar chains in a [[double helix]].]]

In humans, [[eye color]] is an example of an inherited characteristic: an individual might inherit the "brown-eye trait" from one of the parents.<ref>{{cite journal |author=Sturm RA|author2=Frudakis TN |title=Eye colour: portals into pigmentation genes and ancestry |journal=Trends Genet. |volume=20 |issue=8 |pages=327–332 |date=2004 |pmid=15262401 |doi=10.1016/j.tig.2004.06.010}}</ref> Inherited traits are controlled by [[gene]]s and the complete set of genes within an organism's [[genome]] is called its [[genotype]].<ref name=Pearson_2006>{{cite journal |author=Pearson H |title=Genetics: what is a gene? |journal=Nature |volume=441 |issue=7092 |pages=398–401 |date=2006 |pmid=16724031 |doi=10.1038/441398a |bibcode = 2006Natur.441..398P |s2cid=4420674|doi-access=free }}</ref>

The complete set of observable traits of the structure and behavior of an organism is called its [[phenotype]]. These traits arise from the interaction of the organism's genotype with the [[Environment (biophysical)|environment]].<ref>{{cite journal |author=Visscher PM|author2=Hill WG|author3=Wray NR |title=Heritability in the genomics era&nbsp;– concepts and misconceptions |journal=Nat. Rev. Genet. |volume=9 |issue=4 |pages=255–266 |date=2008 |pmid=18319743 |doi=10.1038/nrg2322 |s2cid=690431}}</ref> As a result, many aspects of an organism's phenotype are not inherited. For example, [[sun tanning|suntanned]] skin derives from the interaction between a person's genotype and sunlight;<ref>{{cite journal | title=PGC-1 coactivators regulate MITF and the tanning response | author=Shoag J | journal=Mol Cell |date=Jan 2013 | volume=49 | issue=1 | pages=145–157 | doi=10.1016/j.molcel.2012.10.027 | pmid=23201126 | last2=Haq | first2=Rizwan | last3=Zhang | first3=Mingfeng | last4=Liu | first4=Laura | last5=Rowe | first5=Glenn C. | last6=Jiang | first6=Aihua | last7=Koulisis | first7=Nicole | last8=Farrel | first8=Caitlin | last9=Amos | first9=Christopher I.| display-authors=1 | pmc=3753666}}</ref> thus, suntans are not passed on to people's children. However, some people tan more easily than others, due to differences in their genotype:<ref>{{cite journal | url=http://www.minervamedica.it/en/journals/dermatologia-venereologia/article.php?cod=R23Y2010N01A0037 | title=Genetics of pigmentation and melanoma predisposition | author=Pho LN | author2=Leachman SA | journal=G Ital Dermatol Venereol | date=Feb 2010 | volume=145 | issue=1 | pages=37–45 | pmid=20197744 | access-date=2013-03-26 | archive-date=2019-03-28 | archive-url=https://web.archive.org/web/20190328215053/http://www.minervamedica.it/en/journals/dermatologia-venereologia/article.php?cod=R23Y2010N01A0037 | url-status=live}}</ref> a striking example is people with the inherited trait of [[albinism]], who do not tan at all and are very sensitive to [[sunburn]].<ref>{{cite journal |author=Oetting WS|author2=Brilliant MH|author3=King RA |title=The clinical spectrum of albinism in humans and by action  |journal=Molecular Medicine Today |volume=2 |issue=8 |pages=330–335 |date=1996 |pmid=8796918 |doi=10.1016/1357-4310(96)81798-9}}</ref>

Heritable traits are known to be passed from one generation to the next via [[DNA]], a [[molecule]] that encodes genetic information.<ref name=Pearson_2006/> DNA is a long [[polymer]] that incorporates four types of [[Base pair|bases]], which are interchangeable. The [[Nucleic acid sequence]] (the sequence of bases along a particular DNA molecule) specifies the genetic information: this is comparable to a sequence of letters spelling out a passage of text.<ref>{{cite book |last=Griffiths |first=Anthony, J.F. |title=Introduction to Genetic Analysis |date=2012 |publisher=W.H. Freeman and Company |location=New York |isbn=978-1-4292-2943-2 | page=3 |edition=10th |author2=Wessler, Susan R. |author3=Carroll, Sean B. |author4=Doebley J}}</ref> Before a cell divides through [[mitosis]], the DNA is copied, so that each of the resulting two cells will inherit the DNA sequence. A portion of a DNA molecule that specifies a single functional unit is called a [[gene]]; different genes have different sequences of bases. Within [[cell (biology)|cells]], the long strands of DNA form condensed structures called [[chromosome]]s. Organisms inherit genetic material from their parents in the form of [[homologous chromosome]]s, containing a unique combination of DNA sequences that code for genes. The specific location of a DNA sequence within a chromosome is known as a [[locus (genetics)|locus]]. If the DNA sequence at a particular locus varies between individuals, the different forms of this sequence are called [[allele]]s. DNA sequences can change through [[mutation]]s, 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>{{cite book |last=Futuyma |first=Douglas J. |author-link=Douglas J. Futuyma |date=2005 |title=Evolution |publisher=Sinauer Associates, Inc. |location=Sunderland, Massachusetts |isbn=978-0-87893-187-3 |url-access=registration |url=https://archive.org/details/evolution0000futu}}</ref>

However, while this simple correspondence between an allele and a trait works in some cases, most traits are more complex and are controlled by [[quantitative trait locus|multiple interacting genes]] within and among organisms.<ref>{{cite journal |author=Phillips PC |title=Epistasis – the essential role of gene interactions in the structure and evolution of genetic systems |journal=Nat. Rev. Genet. |volume=9 |issue=11 |pages=855–867 |date=2008 |pmid=18852697 |doi=10.1038/nrg2452 |pmc=2689140}}</ref><ref name=Lin>{{cite journal |author=Wu R|author2=Lin M |title=Functional mapping&nbsp;– how to map and study the genetic architecture of dynamic complex traits |journal=Nat. Rev. Genet. |volume=7 |issue=3 |pages=229–237 |date=2006 |pmid=16485021 |doi=10.1038/nrg1804 |s2cid=24301815}}</ref> Developmental biologists suggest that complex interactions in genetic networks and communication among cells can lead to heritable variations that may underlie some of the mechanics in [[developmental plasticity]] and [[Canalisation (genetics)|canalization]].<ref name="Jablonka02">{{cite journal|last1=Jablonka |first1=E. |last2=Lamb |first2=M.J. |title=The changing concept of epigenetics |journal=Annals of the New York Academy of Sciences |volume=981 |issue=1 |pages=82–96 |date=2002 |url=http://a-c-elitzur.co.il/uploads/articlesdocs/Jablonka.pdf |doi=10.1111/j.1749-6632.2002.tb04913.x |pmid=12547675 |bibcode=2002NYASA.981...82J |s2cid=12561900 |url-status=dead |archive-url=https://web.archive.org/web/20110511122654/http://a-c-elitzur.co.il/uploads/articlesdocs/Jablonka.pdf |archive-date=2011-05-11}}</ref>

Recent findings have confirmed important examples of heritable changes that cannot be explained by direct agency of the DNA molecule. These phenomena are classed as [[epigenetic]] inheritance systems that are causally or independently evolving over genes. Research into modes and mechanisms of epigenetic inheritance is still in its scientific infancy, but this area of research has attracted much recent activity as it broadens the scope of [[heritability]] and evolutionary biology in general.<ref name="Jablonk09">{{cite journal|last1=Jablonka|first1=E.|last2=Raz|first2=G.|title=Transgenerational epigenetic inheritance: Prevalence, mechanisms, and implications for the study of heredity and evolution|journal=The Quarterly Review of Biology|volume=84|issue=2|pages=131–176|date=2009|url=http://compgen.unc.edu/wiki/images/d/df/JablonkaQtrRevBio2009.pdf|pmid=19606595|doi=10.1086/598822|citeseerx=10.1.1.617.6333|s2cid=7233550|access-date=2011-02-18|archive-date=2011-07-15|archive-url=https://web.archive.org/web/20110715111243/http://compgen.unc.edu/wiki/images/d/df/JablonkaQtrRevBio2009.pdf|url-status=live}}</ref> [[DNA methylation]] marking [[chromatin]], self-sustaining [[Metabolism#Evolution|metabolic loops]], gene silencing by [[RNA interference]], and the three dimensional [[Protein structure|conformation]] of proteins (such as [[prions]]) are areas where epigenetic inheritance systems have been discovered at the organismic level.<ref name="Bossdorf10">{{cite journal|last1=Bossdorf|first1=O.|last2=Arcuri|first2=D.|last3=Richards|first3=C.L.|last4=Pigliucci|first4=M.|title=Experimental alteration of DNA methylation affects the phenotypic plasticity of ecologically relevant traits in ''Arabidopsis thaliana''|journal=Evolutionary Ecology|volume=24|issue=3|pages=541–553|date=2010|doi=10.1007/s10682-010-9372-7|s2cid=15763479|url=https://boris.unibe.ch/5317/1/10682_2010_Article_9372.pdf|access-date=2019-08-15|archive-date=2020-03-01|archive-url=https://web.archive.org/web/20200301011727/https://boris.unibe.ch/5317/1/10682_2010_Article_9372.pdf|url-status=live}}</ref><ref name="Jablonka05">{{cite book|last1=Jablonka|first1=E.|last2=Lamb|first2=M.|title=Evolution in four dimensions: Genetic, epigenetic, behavioural, and symbolic|date=2005|publisher=MIT Press|url=https://books.google.com/books?id=EaCiHFq3MWsC|isbn=978-0-262-10107-3|access-date=2015-06-27|archive-date=2021-12-27|archive-url=https://web.archive.org/web/20211227223526/https://books.google.com/books?id=EaCiHFq3MWsC|url-status=live}}</ref> Heritability may also occur at even larger scales. For example, ecological inheritance through the process of [[niche construction]] is defined by the regular and repeated activities of organisms in their environment. This generates a legacy of effect that modifies and feeds back into the selection regime of subsequent generations. Descendants inherit genes plus environmental characteristics generated by the ecological actions of ancestors.<ref name="Laland06">{{cite journal|title=Perspective: Seven reasons (not) to neglect niche construction|last1=Laland|first1=K.N.|last2=Sterelny|first2=K.|journal=Evolution|volume=60|issue=8|pages=1751–1762|date=2006|doi=10.1111/j.0014-3820.2006.tb00520.x|pmid=17089961|doi-access=free}}</ref> Other examples of heritability in evolution that are not under the direct control of genes include the inheritance of [[Dual inheritance theory|cultural traits]], [[group selection|group heritability]], and [[symbiogenesis]].<ref name="Chapman98">{{cite journal|title=Morphogenesis by symbiogenesis |last1=Chapman |first1=M.J. |last2=Margulis |first2=L. |author2-link=Lynn Margulis |journal=International Microbiology |volume=1 |issue=4 |pages=319–326 |date=1998 |url=http://www.im.microbios.org/04december98/14%20Chapman.pdf |pmid=10943381 |url-status=dead |archive-url=https://web.archive.org/web/20140823062546/http://www.im.microbios.org/04december98/14%20Chapman.pdf |archive-date=2014-08-23}}</ref><ref name="Wilson07" /><ref name="Bijma08">{{cite journal|last1=Bijma|first1=P.|last2=Wade|first2=M.J.|title=The joint effects of kin, multilevel selection and indirect genetic effects on response to genetic selection|journal=Journal of Evolutionary Biology|volume=21|issue=5|pages=1175–1188|date=2008|pmid=18547354|doi=10.1111/j.1420-9101.2008.01550.x|s2cid=7204089|doi-access=free}}</ref> These examples of heritability that operate above the gene are covered broadly under the title of [[multilevel selection|multilevel or hierarchical selection]], which has been a subject of intense debate in the history of evolutionary science.<ref name="Wilson07">{{cite journal|last1=Wilson|first1=D. S.|last2=Wilson|first2=E.O.|title=Rethinking the theoretical foundation of sociobiology|journal=The Quarterly Review of Biology|volume=82|issue=4|date=2007|url=http://evolution.binghamton.edu/dswilson/wp-content/uploads/2010/01/Rethinking-sociobiology.pdf|doi=10.1086/522809|pages=327–348|pmid=18217526|s2cid=37774648|url-status=dead|archive-url=https://web.archive.org/web/20110511235639/http://evolution.binghamton.edu/dswilson/wp-content/uploads/2010/01/Rethinking-sociobiology.pdf|archive-date=2011-05-11}}</ref><ref name="Vrba86">{{cite journal |title=The hierarchical expansion of sorting and selection: Sorting and selection cannot be equated |last1=Vrba |first1=E.S. |last2=Gould |first2=S.J. |journal=Paleobiology |volume=12 |issue=2 |pages=217–228 |date=1986 |url=http://www.explorelifeonearth.org/cursos/VrbaGould1986sorting.pdf |doi=10.1017/S0094837300013671 |bibcode=1986Pbio...12..217V |s2cid=86593897 |access-date=2011-02-18 |archive-date=2016-08-04 |archive-url=https://web.archive.org/web/20160804063711/http://www.explorelifeonearth.org/cursos/VrbaGould1986sorting.pdf |url-status=usurped}}</ref>