See soorce fer Genetics

'''Genetics''' (frae the [[Auncient Greek]] {{lang|grc|γενετικός}} ''{{lang|grc-Latn|genetikos}}'' meanin "genitive"/"generative", in turn frae {{lang|grc|γένεσις}} ''{{lang|grc-Latn|genesis}}'' meanin "oreegin"),<!--
     --><ref name="Genetikos γενετ-ικός">{{cite web |url=http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3D%2321880&redirect=true |title=Genetikos (γενετ-ικός) |work=Henry George Liddell, Robert Scott, A Greek-English Lexicon |publisher=Perseus Digital Library, Tufts University |accessdate=20 February 2012}}</ref><!--
     --><ref name="Genesis γένεσις">{{cite web |url=http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3D%2321873&redirect=true |title=Genesis (γένεσις) |work=Henry George Liddell, Robert Scott, A Greek-English Lexicon |publisher=Perseus Digital Library, Tufts University |accessdate=20 February 2012}}</ref><!--
     --><ref name="Genetic">{{cite web |url=http://www.etymonline.com/index.php?search=Genetic&searchmode=none |title=Genetic |publisher=Online Etymology Dictionary |accessdate=20 February 2012}}</ref> <!--
 -->a field in [[biology]], is the science o [[gene]]s, [[heredity]], an [[Genetic variation|variation]] in livin [[organism]]s.<ref name=griffiths2000sect60>{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.60 |chapter=Genetics and the Organism: Introduction}}</ref><ref name=Hartl_and_Jones>Hartl D, Jones E (2005)</ref>

The faither o genetics is [[Gregor Mendel]], a late 19t-century scientist an [[Augustinian]] [[monk|freear]]. Mendel studied "trait inheritance", patterns in the wey traits are haundit doun frae paurents tae affspring. He observed that organisms (pease plants) inherit traits bi wey o discrete "units o inheritance". This term, still uised the day, is a somewhit ambiguous definition o whit is referred tae as a [[gene]].

[[Phenotypic trait|Trait]] inheritance an [[Molecular genetics|molecular]] inheritance mechanisms o genes are still primar principles o genetics in the 21st century, but modren genetics haes expaundit ayont inheritance tae studyin the function an behaviour o genes. Gene structur andfunction, variation, an distribution are studied within the context o the [[Cell (biology)|cell]], the organism (e.g. [[Dominance (genetics)|dominance]]), an within the context o a population. Genetics haes gien rise tae a nummer o subfields, includin [[epigenetics]] an [[population genetics]]. Organisms studied within the broad field span the domeen o life, includin [[bacteria]], [[plant]]s, [[ainimal]]s, an [[human]]s.

Genetic processes wark in combination wi an organism's environment an experiences tae influence development an [[behavioural genetics|behaviour]], eften referred tae as [[naitur versus nurtur]]. The [[intracellular]] or [[extracellular]] environment o a cell or organism mey switch gene transcription on or off. A clessic ensaumple is twa seeds o genetically identical maize, ane placed in a temperate climate an ane in an arid climate. While the average hicht o the twa maize stauks mey be genetically determined tae be equal, the ane in the [[arid climate]] anerly growes tae hauf the hicht o the ane in the temperate climate due tae lack o watter an nutrients in its environment.

==Etymology==
The wird ''genetics'' stems frae the [[auncient Greek]] {{lang|grc|γενετικός}} ''{{lang|grc-Latn|genetikos}}'' meanin "genitive"/"generative", that in turn derives frae {{lang|grc|γένεσις}} ''{{lang|grc-Latn|genesis}}'' meanin "oreegin".<ref name="Genetikos γενετ-ικός"/><ref name="Genesis γένεσις"/><ref name="Genetic"/>

==History==
[[File:DNA Overview2.png|thumb|right|140px|upright|[[DNA]], the molecular basis for [[Heredity|biological heirship]]. Ilk straund o DNA is a cheen o [[nucleotide]]s, matchin ilk ither in the centre tae form whit leuk lik rungs on a twisted ledder.]]

The observation that leevin things faw heir tae [[Phenotypic trait|trait]]s frae thair parents haes been uised syne prehistoric times tae impruive crap plants an ainimals throu [[selective breedin]].<ref name="Publishing2009">{{cite book |author=DK Publishing |title=Science: The Definitive Visual Guide |url=https://books.google.com/books?id=sFiJFuzRVFQC&pg=PA362 |year=2009 |publisher=Penguin |isbn=978-0-7566-6490-9 |page=362}}</ref> The modren science o genetics, seekin tae unnerstaund this process, begoud wi the wark o the [[Augustinian]] [[freear]] [[Gregor Mendel]] in the mid-19t century.<ref name=Weiling>{{cite journal |pmid=1887835| doi=10.1002/ajmg.1320400103 |year=1991 |last1=Weiling |first1=F |title=Historical study: Johann Gregor Mendel 1822–1884. |volume=40 |issue=1 |pages=1–25; discussion 26 |journal=American Journal of Medical Genetics}}</ref>

Prior tae Mendel, [[Imre Festetics]], a [[Hungary|Hungarian]] noble, wha lived in Kőszeg afore Mendel, wis the first wha uised the wird "genetics." He descrived several rules o genetic heirship in his wirk ''The genetic law o the Naitur'' (Die genetische Gesätze der Natur, 1819). His seicont law is the same as whit Mendel published. In his third law, he developed the basic principles o mutation (he can be conseedert a forerunner o Hugo de Vries).<ref>{{cite journal|year=2014|title=Imre Festetics and the Sheep Breeders' Society of Moravia: Mendel's Forgotten "Research Network" |url=http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001772|journal=PLoS Biology|volume=12|issue=1|page=e1001772 |doi=10.1371/journal.pbio.1001772 |author1=Poczai P. |author2=Bell N. |author3=Hyvönen J.|pmid=24465180|pmc=3897355}}</ref>

Modren genetics stairtit wi Mendel's studies o the naitur o heirship in plants. In his paper "''Versuche über Pflanzenhybriden''" ("[[Experiments on Plant Hybridisation]]"), presentit in 1865 tae the ''Naturforschender Verein'' (Society for Resairch in Naitur) in [[Brünn]], Mendel traced the heirship patterns o certaint traits in pease plants an descrived them mathematically.<ref name="mendel">{{cite web |title= Mendel's Paper in English |url=http://www.mendelweb.org/Mendel.html |first=Roger B. |last=Blumberg}}</ref> Awtho this pattern o heirship coud anerly be observed for a few traits, Mendel's wark suggestit that heirship wis pairticulate, nae acquired, an that the heirship patterns o mony traits coud be explained throu semple rules an ratios.

The importance o Mendel's wirk did nae gain wide unnderstaundin till 1900, efter his daith, whan [[Hugo de Vries]] an ither scientists rediscovered his resairch. [[William Bateson]], a proponent o Mendel's wark, mentioned the wird ''genetics'' in 1905<ref>genetics, ''n.'', [[Oxford English Dictionary]], 3rd ed.</ref><ref>{{cite web |url=http://www.jic.ac.uk/corporate/about/bateson.htm |title=Letter from William Bateson to Alan Sedgwick in 1905 |publisher=The John Innes Centre |accessdate=15 March 2008 |author=Bateson W |deadurl=yes |archiveurl=https://web.archive.org/web/20071013020831/http://www.jic.ac.uk/corporate/about/bateson.htm |archivedate=13 October 2007 |df=dmy-all }} Note that the letter was to an Adam Sedgwick, a zoologist and "Reader in Animal Morphology" at [[Trinity College, Cambridge]]</ref> (the adjective ''genetic'', derived frae the Greek wird ''genesis''—γένεσις, "oreegin", predates the noun an wis first uised in a biological sense in 1860<ref>genetic, ''adj.'', Oxford English Dictionary, 3rd ed.</ref>).

===Molecular genetics===
Awtho genes war kent tae exist on chromosomes, chromosomes are componed o baith protein an DNA, an scientists did nae ken that o the twa is responsible for heirship. In 1928, [[Frederick Griffith]] discovered the phenomenon o [[Transformation (genetics)|transformation]] (see [[Griffith's experiment]]): deid bacteria coud transfer [[genetic material]] tae "transform" ither still-leevin bacteria. Saxteen years later, in 1944, the [[Avery–MacLeod–McCarty experiment]] identifee'd DNA as the molecule responsible for transformation.<ref name=Avery_et_al>{{cite journal |doi=10.1084/jem.79.2.137 |last1=Avery |first1=OT |last2=MacLeod |first2=CM |last3=McCarty |first3=M |title=Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III |journal=The Journal of Experimental Medicine |volume=79 |issue=2 |pages=137–58 |year=1944 |pmid=19871359 |pmc=2135445}} Reprint: {{cite journal |pmid=33226 |year=1979 |last1=Avery |first1=OT |last2=MacLeod |last3=McCarty |title=Studies on the chemical nature of the substance inducing transformation of pneumococcal types. Inductions of transformation by a desoxyribonucleic acid fraction isolated from pneumococcus type III |volume=149 |issue=2 |pages=297–326 |journal=The Journal of Experimental Medicine |doi=10.1084/jem.149.2.297 |first2=CM |first3=M |pmc=2184805}}</ref>

[[James Watson]] an [[Francis Crick]] determined the structur o DNA in 1953, uisin the [[X-ray crystallografie]] wark o [[Rosalind Franklin]] an [[Maurice Wilkins]] that indicatit DNA haes a [[Helix|helical]] structur (i.e., shapit lik a corkscrew).<ref>{{cite book |title=The Eighth Day of Creation: Makers of the Revolution in Biology |last=Judson |first=Horace |authorlink=Horace Freeland Judson |year=1979 |publisher=Cold Spring Harbor Laboratory Press |isbn=0-87969-477-7 |pages=51–169}}</ref><ref name=watsoncrick_1953a>{{cite journal |url=http://www.nature.com/nature/dna50/watsoncrick.pdf |doi=10.1038/171737a0 |title=Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid |year=1953 |last1=Watson |first1=J. D. |last2=Crick |journal=Nature |volume=171 |pages=737–8 |pmid=13054692 |first2=FH |issue=4356 |bibcode=1953Natur.171..737W}}</ref> Thair dooble-helix model haed twa strands o DNA wi the nucleotides pyntin inward, each matching a complementary nucleotide on the ither strand tae form what leuk lik rungs on a twisted ladder.<ref name=watsoncrick_1953b>{{cite journal |url=http://www.nature.com/nature/dna50/watsoncrick2.pdf |doi=10.1038/171964b0 |title=Genetical Implications of the Structure of Deoxyribonucleic Acid |year=1953 |last1=Watson |first1=J. D. |last2=Crick |journal=Nature |volume=171 |pages=964–7 |pmid=13063483 |first2=FH |issue=4361 |bibcode=1953Natur.171..964W}}</ref>

==Featurs o heirship==
===Discrete heirship an Mendel's laws===
At its maist fundamental level, heirship in organisms occurs bi passin discrete heritable units, cried [[gene]]s, frae paurents tae affspring.<ref name=griffiths2000sect199>{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.199 |chapter=Patterns of Inheritance: Introduction}}</ref> This property wis first observed bi [[Gregor Mendel]], wha studied the segregation o heritable traits in [[pease]] plants.<ref name="mendel" /><ref name=griffiths2000sect200>{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.200 |chapter=Mendel's experiments}}</ref> In his experiments studyin the trait for flouer colour, Mendel observed that the flouers o ilk pease plant war aither purpie or white—but niver an intermediate atween the twa colours. Thir different, discrete versions o the same gene are cried [[allele]]s.

In the case o the pease, that is a [[diploid]] species, ilk individual plant haes twa copies o ilk gene, ane copy inheritit frae ilk parent.<ref name=griffiths2000sect484/> Mony species, includin humans, hae this pattern o heirship. Diploid organisms wi twa copies o the same allele o a gien gene are cried [[homozygous]] at that [[Locus (genetics)|gene locus]], while organisms wi twa different alleles o a gien gene are cried [[heterozygous]].

The set o alleles for a gien organism is cried its [[genoteep]], while the observable traits o the organism are cried its [[phenoteep]]. When organisms are heterozygous at a gene, eften ane allele is cried [[Dominant allele|dominant]] as its qualities dominate the phenoteep o the organism, while the ither allele is cried [[Recessive allele|recessive]] as its qualities recede an are nae observed. Some alleles dae nae hae complete dominance an insteid hae [[Dominance relationship#Incomplete an semi-dominance|incomplete dominance]] bi expressin an intermediate phenoteep, or [[Dominance relationship#Co-dominance|codominance]] bi expressin baith alleles at ance.<ref name=griffiths2000sect630>{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.630 |chapter=Interactions between the alleles of one gene}}</ref>

===Multiple gene interactions===
[[File:Galton-height-regress.png|thumb|right|Human height is a trait wi complex genetic causes. [[Francis Galton]]'s data frae 1889 shaws the relationship atween affspring hicht as a function o mean paurent hicht. ]]
Organisms hae thoosands o genes, an in sexually reproducin organisms thir genes generally assort independently o ilk ither. This means that the inheritance o an allele for yellae or green pease colour is unrelatit tae the inheritance o alleles for white or purpie flouers. This phenomenon, kent as "[[Mendelian inheritance#Law o Independent Assortment (The "Seicont Law")|Mendel's seicont law]]" or the "law o independent assortment," means that the alleles ofdifferent genes get shuffled atween paurents tae form affspring wi mony different combinations. (Some genes dae nae assort independently, demonstratin [[genetic linkage]], a tapic discussed later in this airticle.)

Eften different genes can interact in a wey that influences the same trait. In the [[Blue-eed Mary]] (''Omphalodes verna''), for ensaumple, thare exeests a gene wi alleles that determine the colour o flouers: blue or magenta. Anither gene, houever, controls whither the flouers hae colour at aw or are white. Whan a plant haes twa copies o this white allele, its flouers are white—regairdless o whither the first gene haes blue or magenta alleles. This interaction atween genes is cried [[epistasis]], wi the seicont gene epistatic tae the first.<ref name=griffiths2000sect644>{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.644 |chapter=Gene interaction and modified dihybrid ratios}}</ref>

Mony traits are nae discrete featurs (e.g. purpie or white flouers) but are insteid conteenous featurs (e.g. human hicht an [[Human skin colour|skin colour]]). Thir [[Quantitative trait locus|complex traits]] are products o mony genes.<ref>{{cite journal |pmid=15931374 |doi=10.1172/JCI25421 |year=2005 |last1=Mayeux |first1=R |title=Mapping the new frontier: complex genetic disorders |volume=115 |issue=6 |pages=1404–7 |journal=The Journal of Clinical Investigation |pmc=1137013}}</ref> The influence o thir genes is mediatit, tae varyin degrees, bi the environment an organism haes experienced. The degree tae which an organism's genes contreibute tae a complex trait is cried [[heritability]].<ref name=griffiths2000sect4009>{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.4009 |chapter=Quantifying heritability}}</ref> Meisurment o the heritability o a trait is relative—in a mair variable environment, the environment haes a bigger influence on the tot variation o the trait. For ensaumple, human hicht is a trait wi complex causes. It haes a heritability o 89% in the Unitit States. In Nigerie, houever, whaur fowk experience a mair variable access tae guid nutreetion an [[heal care]], hicht haes a heritability o anerly 62%.<ref>{{cite journal|last2=Guo|first2=X|last3=Adeyemo|first3=AA|last4=Wilks|first4=R|last5=Forrester|first5=T|last6=Lowe Jr|first6=W|last7=Comuzzie|first7=AG|last8=Martin|first8=LJ|last9=Zhu|first9=X|year=2001|title=Heritability of obesity-related traits among Nigerians, Jamaicans and US black people|journal=International Journal of Obesity and Related Metabolic Disorders|volume=25|issue=7|pages=1034–41|doi=10.1038/sj.ijo.0801650|pmid=11443503|last1=Luke|first1=A|last10=Rotimi|last11=Cooper|first10=CN|first11=RS}}</ref>

==Molecular basis for inheritance==

===DNA an chromosomes===
{{main article|DNA|Chromosome}}
[[File:DNA chemical structure.svg|thumb|right|The [[molecular structur]] o DNA. Bases pair throu the arrangement o [[hydrogen bondin]] atween the straunds.]]
The [[Molecule|molecular]] basis for genes is [[deoxyribonucleic acid]] (DNA). DNA is componed o a cheen o [[nucleotide]]s, o that thare are fower teeps: [[adenine]] (A), [[cytosine]] (C), [[guanine]] (G), an [[thymine]] (T). Genetic information exeests in the sequence o thir nucleotides, an genes exeest as stretches o sequence alang the DNA cheen.<ref name=Pearson_2006>{{cite journal |pmid=16724031 |doi=10.1038/441398a |year=2006 |last1=Pearson |first1=H |title=Genetics: what is a gene? |volume=441 |issue=7092 |pages=398–401 |journal=Nature |bibcode=2006Natur.441..398P}}</ref> [[Virus]]es are the anerly exception tae this rule—whiles viruses uise the verra seemilar molecule [[RNA]] insteid o DNA as thair genetic material.<ref>{{cite book |title=Microbiology |url=https://archive.org/details/microbiology0001pres |last=Prescott |first=L |year=1993 |publisher=Wm. C. Brown Publishers |isbn=0-697-01372-3}}</ref> Viruses canna reproduce withoot a [[Host (biology)|host]] an are unaffectit bi mony genetic processes, sae tend nae tae be conseedert leevin organisms.

DNA normally exeests as a dooble-straundit molecule, cyled intae the shape o a [[dooble helix]]. Ilk nucleotide in DNA preferentially pairs wi its pairtner nucleotide on the opposite straund: A pairs wi T, an C pairs wi G. Sicweys, in its twa-straundit form, ilk straund effectively conteens aw necessar information, redundant wi its pairtner straund. This structur o DNA is the pheesical basis for heirship: [[DNA replication]] duplicates the genetic information bi splittin the straunds an uisin ilk straund as a template for synthesis o a new pairtner straund.<ref name=griffiths2000sect1523>{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.1523 |chapter=Mechanism of DNA Replication}}</ref>

Genes are arranged linearly alang lang cheens o DNA base-pair sequences. In [[bacteria]], ilk cell uisually conteens a single circular [[Nucleoid|genophore]], while [[Eukaryote|eukaryotic]] organisms (sic as plants an ainimals) hae thair DNA arranged in multiple linear chromosomes. Thir DNA strands are eften extremely lang; the lairgest human chromosome, for ensaumple, is aboot 247 million [[base pair]]s in lenth.<!--
     --><ref>{{cite journal |doi=10.1038/nature04727 |pmid=16710414 |year=2006 |last1=Gregory |first1=SG |last2=Barlow |last3=McLay |last4=Kaul |last5=Swarbreck |last6=Dunham |last7=Scott |last8=Howe |last9=Woodfine |displayauthors=8 |title=The DNA sequence and biological annotation of human chromosome 1 |volume=441 |issue=7091 |pages=315–21 |journal=Nature |first2=KF |first3=KE |first4=R |first5=D |first6=A |first7=CE |first8=KL |first9=K|bibcode = 2006Natur.441..315G |last10=Spencer |first10=C. C. A. |last11=Jones |first11=M. C. |last12=Gillson |first12=C. |last13=Searle |first13=S. |last14=Zhou |first14=Y. |last15=Kokocinski |first15=F. |last16=McDonald |first16=L. |last17=Evans |first17=R. |last18=Phillips |first18=K. |last19=Atkinson |first19=A. |last20=Cooper |first20=R. |last21=Jones |first21=C. |last22=Hall |first22=R. E. |last23=Andrews |first23=T. D. |last24=Lloyd |first24=C. |last25=Ainscough |first25=R. |last26=Almeida |first26=J. P. |last27=Ambrose |first27=K. D. |last28=Anderson |first28=F. |last29=Andrew |first29=R. W. |last30=Ashwell |first30=R. I. S.}}</ref> <!--
 -->The DNA o a chromosome is associatit wi structural proteins that organize, compact, an control access tae the DNA, formin a material cried [[chromatin]]; in eukaryotes, chromatin is uisually componed o [[nucleosome]]s, segments o DNA woond aroond cores o [[histone]] proteins.<ref>Alberts et al. (2002), [https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.section.608 II.4. DNA and chromosomes: Chromosomal DNA and Its Packaging in the Chromatin Fiber]</ref> The full set o hereditary material in an organism (uisually the combined DNA sequences o aw chromosomes) is cried the [[genome]].

While [[haploid]] organisms hae anerly ane copy o ilk chromosome, maist ainimals an mony plants are [[diploid]], conteenin twa o ilk chromosome an sicweys twa copies o ivery gene.<ref name=griffiths2000sect484>{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.484 |chapter=Mendelian genetics in eukaryotic life cycles}}</ref>

Mony species hae sae-cried [[sex chromosome]]s that determine the gender o ilk organism.<ref name=griffiths2000sect222>{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.222 |chapter=Sex chromosomes and sex-linked inheritance}}</ref> In humans an mony ither ainimals, the [[Y chromosome]] conteens the gene that triggers the development o the speceefically male chairactereestics.

===Reproduction===
When cells divide, thair full genome is copied an ilk [[Cell diveesion|dauchter cell]] inherits ane copy. This process, cried [[mitosis]], is the semplest form o reproduction an is the basis for [[asexual reproduction]]. Asexual reproduction can an aa occur in multicellular organisms, producin affspring that inherit thair genome frae a single paurent. Affspring that are genetically identical tae thair paurents are cried [[Clonin|clones]].

[[Eukaryote|Eukaryotic]] organisms eften uise [[sexual reproduction]] tae generate affspring that conteen a mixtur o genetic material inheritit frae twa different paurents. The process o sexual reproduction alternates atween forms that conteen single copies o the genome ([[haploid]]) an dooble copies ([[diploid]]).<ref name=griffiths2000sect484/>

==Gene expression==

===Genetic code===
[[File:Genetic code.svg|thumb|left|The [[genetic code]]: Uisin a [[Genetic code#Discovery|triplet code]], DNA, throu a [[messenger RNA]] intermediary, specifees a protein.]]
Genes generally [[Gene expression|express]] thair functional effect throu the production o [[protein]]s, that are complex molecules responsible for maist functions in the cell. Proteins are made up o ane or mair polypeptide cheens, ilk o that is componed o a sequence o [[amino acid]]s, an the DNA sequence o a gene (throu an RNA intermediate) is uised tae produce a speceefic [[peptide sequence|amino acid sequence]]. This process begins wi the production o an [[RNA]] molecule wi a sequence matchin the gene's DNA sequence, a process cried [[Transcription (genetics)|transcription]].

This [[messenger RNA]] molecule is then uised tae produce a correspondin amino acid sequence throu a process cried [[translation (biology)|translation]]. Ilk group o three nucleotides in the sequence, cried a [[codon]], corresponds aither tae ane o the twinty possible amino acids in a protein or an [[stap codon|instruction tae end the amino acid sequence]]; this correspondence is cried the [[genetic code]].<ref>{{cite book |title=Biochemistry |vauthors=Berg JM, Tymoczko JL, Stryer L, Clarke ND |edition=5th |year=2002 |publisher=W. H. Freeman and Company |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=stryer.section.685 |chapter=I. 5. DNA, RNA, and the Flow of Genetic Information: Amino Acids Are Encoded by Groups of Three Bases Starting from a Fixed Point}}</ref>

===Naitur an nurtur===
{{main article|Naitur an nurtur}}
[[File:Niobe050905-Siamese Cat.jpeg|thumb|upright|[[Siamese (cat)|Siamese cat]]s hae a temperature-sensitive pigment-production mutation.]]
Awtho genes conteen aw the information an organism uises tae function, the environment plays an important role in determinin the ultimate phenoteeps an organism displays. The phrase "[[naitur an nurtur]]"  refers tae this complementary relationship. The phenoteep o an organism depends on the interaction o genes an the environment. An interestin ensaumple is the coat colouration o the [[Siamese (cat)|Siamese cat]]. In this case, the bouk temperatur o the cat plays the role o the environment. The cat's genes code for daurk hair, sicweys the hair-producin cells in the cat mak cellular proteins resultin in daurk hair. But thir daurk hair-producin proteins are sensitive tae temperatur (i.e. hae a mutation causin temperature-sensitivity) an [[Denaituration (biochemistry)|denaitur]] in heicher-temperatur environments, failin tae produce daurk-hair pigment in auries whaur the cat haes a heicher bouk temperatur. In a law-temperatur environment, houever, the protein's structureis stable an produces daurk-hair pigment normally. The protein remeens functional in auries o skin that are caulder{{emdash}}sic as its legs, lugs, tail an face{{emdash}}sae the cat haes daurk-hair at its extremities.<ref>{{cite journal|last2=Geary|first2=LA|last3=Grahn|first3=RA|last4=Lyons|first4=LA|year=2006|title=Albinism in the domestic cat (''Felis catus'') is associated with a tyrosinase (TYR) mutation|journal=Animal Genetics|volume=37|issue=2|pages=175–8|doi=10.1111/j.1365-2052.2005.01409.x|pmc=1464423|pmid=16573534|last1=Imes|first1=DL}}</ref>

==Genetic cheenge==

===Mutations===
{{main article|Mutation}}
[[File:Gene-duplication.png|thumb|upright|Gene duplication allous diversification bi providin redundancy: ane gene can mutate an lose its oreeginal function withoot haurmin the organism.]]
In the process o [[DNA replication]], errors occasionally occur in the polymerisation o seicont strand. Thir errors, cried [[mutation]]s, can affect the phenoteep o an organism, especially if thay occur within the protein codin sequence o a gene. Error rates are uisually verra law—1 error in ivery 10–100&nbsp;million bases—due tae the "pruifreadin" ability o [[DNA polymerase]]s.<!--
     --><ref name="griffiths2000sect2706">{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.2706 |chapter=Spontaneous mutations}}</ref><!--
     --><ref name="Kunkel">{{cite journal |doi=10.1038/sj.emboj.7600158 |pmid=15057282 |year=2004 |last1=Freisinger |first1=E |last2=Grollman |last3=Miller |last4=Kisker |title=Lesion (in)tolerance reveals insights into DNA replication fidelity |volume=23 |issue=7 |pages=1494–505 |journal=The EMBO Journal |first2=AP |first3=H |first4=C |pmc=391067}}</ref> <!--
 -->Processes that increase the rate o cheenges in DNA are cried [[mutagenic]]: mutagenic chemicals promote errors in DNA replication, eften bi interferin wi the structur o base-pairin, while [[UV radiation]] induces mutations bi causin damage tae the DNA structur.<!--
     --><ref name="griffiths2000sect2727">{{cite book |editor-first=Anthony J. F. |editor-last=Griffiths |editor2-first=Jeffrey H. |editor2-last=Miller |editor3-first=David T. |editor3-last=Suzuki |editor4-first=Richard C. |editor4-last=Lewontin |editor5-last=Gelbart |title=An Introduction to Genetic Analysis |year=2000 |isbn=0-7167-3520-2 |edition=7th |publisher=W. H. Freeman |location=New York |chapterurl=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=iga.section.2727 |chapter=Induced mutations}}</ref> <!--
 -->Chemical damage tae DNA occurs naiturally as well an cells uise [[DNA repair]] mechanisms tae repair mismatches an breaks. The repair daes nae, houever, alweys restore the oreeginal sequence.

Ower mony generations, the genomes o organisms can cheenge signeeficantly, resultin in [[evolution]]. In the process cried [[adaptation]], selection for beneficial mutations can cause a species tae evolve intae forms better able tae survive in thair environment.<!--
     --><ref name="Darwin">{{cite book |last=Darwin |first=Charles |authorlink=Charles Darwin |year=1859 |title=On the Origin of Species |place=London |publisher=John Murray |edition=1st |pages=1 |url=http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=text&pageseq=16 |isbn=0-8014-1319-2}}<br />Earlier related ideas were acknowledged in {{cite book |last=Darwin |first=Charles |authorlink=Charles Darwin |year=1861 |title=On the Origin of Species |place=London |publisher=John Murray |edition=3rd |pages=xiii |url=http://darwin-online.org.uk/content/frameset?itemID=F381&viewtype=text&pageseq=20 |nopp=true |isbn=0-8014-1319-2}}</ref>

==References==
{{Reflist}}

[[Category:Genetics| ]]