#REDIRECT [[ nl:Junk-DNA]] ▼
I [[molekylærbiologi]] er '''junk-DNA''' eller '''nonsens-DNA''' en samlet benævnelse for [[kromosom]]ers eller [[genom]]ers [[DNA]]-sekvenser, som ikke har en kendt funktion. Op imod 97 % af den [[menneske]]lige genom er blevet klassificeret som "junk" - eller på dansk affald.
<noinclude>Forkortelsen DNA er almindeligt brugt med store bogstaver i alle videnskabelige og undervisningskredse. Almindelig anerkendt internationalt som standard-forkortelse med store bogstaver. Det kan ikke anbefales at lave om på en almindelig brugt og anerkendt forkortelse.</noinclude>
Selvom det meste af junk-DNA sekvenser formodes at være [[evolutionær]]e [[artefakt]]er, som ikke har noget aktuelt formål, tror nogle at junk-DNA fungerer på måder, vi endnu ikke kender betydningen af.
<ref>[http://news.bbc.co.uk/2/hi/science/nature/6749213.stm 14 June 2007, BBC News: Human genome further unravelled] Citat: "...it suggests genes, so called junk DNA and other elements, together weave an intricate control network...He said: "The genome looks like it is far more of a network of RNA transcripts that are all collaborating together. Some go off and make proteins; [and] quite a few, although we know they are there, we really do not have a good understanding of what they do. "This leads to a much more complex picture." The researchers now hope to scale up their efforts to look at the other 99% of the genome..."</ref>
Ydermere kan bibeholdelsen af noget junk-DNA over millioner af års evolution måske betyde, at de har en livsvigtig funktion. Nogle betragter mærkaten "junk" som en forkert benævnelse, mens andre anser junk-DNA som DNA gemt væk til mulig fremtidig anvendelse, i stedet for noget, der skal smides ud. Nogle foretrækker benævnelsen '''ikke-kodende DNA''', selvom junk-DNA ofte indeholder [[transposon]]er, der koder for [[protein]]er uden klar værdi for deres vært. Atter anden dna kommer fra parasitter. Et eksempel er f.eks. at 70% af [[hvirvelløse dyr]] har indlejret store dele eller næsten hele parasitten ''Wolbachia''s [[genom]] i deres genom.
<ref>[http://www.sciencedaily.com/releases/2007/08/070830150118.htm University of Rochester (2007, August 31). One Species' Entire Genome Discovered Inside Another's. ScienceDaily. Retrieved November 10, 2007] Citat: "..."This study establishes the widespread occurrence and high frequency of a process that we would have dismissed as science fiction until just a few years ago," says W. Ford Doolittle, Canada Research Chair in Comparative Microbial Genomics at Dalhousie University, who is not connected to the study. "This is stunning evidence for increased frequency of gene transfer."..."This parasite has implanted itself inside the cells of 70 percent of the world's invertebrates, coevolving with them. And now, we've found at least one species where the parasite's entire or nearly entire genome has been absorbed and integrated into the host's. The host's genes actually hold the coding information for a completely separate species."..."</ref>
[[Videnskab]]en [[funktionel genomik]] har udviklet mange accepterede teknikker til at karakterisere proteinkodende [[gen]]er, [[RNA-gen]]er og regulerende regioner. I det meste af [[plante]]s og [[dyr]]s genomer udgør det proteinkodende DNA kun en mindre procentdel. I menneskets tilfælde mindre end 2 %. Funktionen af resten bliver undersøgt. Meget af det kan identificeres som repeterende DNA-sekvenser uden kendt biologisk funktion for deres vært. Det er dog værdifuldt for [[genetiker]]e, da de kan anvende det til nedarvningsklassifikation. Men når dette er fratrukket junk-DNA, er der stadig store mængder sekvenser, som indtil videre ikke kan klassificeres til andet end "junk".
Et organismes genomstørrelse inkl. junk-DNA ser ud til at have lille sammenhæng med organismets [[kompleksitet]]: Det er blevet rapporteret, at genomet for den encellede organisme ''[[Amoeba]] dubia'' mængdemæssigt indeholder mere end 200 gange så meget dna som menneskets genom"<ref name=Gregory>{{
cite journal
| author=Gregory, T.R. and P.D.N. Hebert .
| title=The modulation of DNA content: proximate causes and ultimate consequences
| journal=Genome Research
| year=1999
| pages=317-324
| volume=9
|
}}</ref>
<ref name=GregoryWeb>Gregory, T.R. (2005). Animal Genome Size Database. http://www.genomesize.com.</ref>.
[[Pindsvinefisk]]en ''[[Japansk kuglefisk|Takifugu]] rubripes'' genom indeholder mængdemæssigt kun 1/10 af menneskets genom, men ser ud til at have ligeså mange brugte gener som menneskets. Det meste af forskellen ser ud til at ligge i det der i dag kaldes junk-DNA.<ref name=Wahls>{{
cite journal
| author=Wahls, W.P., ''et al.''
| title=Hypervariable minisatellite DNA is a hotspot for homologous recombination in human cells
| journal=Cell
| year=1990
| pages=95-103
| volume=60
| issue=1
| id=PMID 2295091
}}</ref>
I nyere tid er der i forskellige organismer blevet fundet vigtige funktioner i DNA, der tidligere var klassificeret som junk-DNA.
<ref>[http://news.bbc.co.uk/1/hi/sci/tech/3703935.stm 12 May, 2004, BBC News: 'Junk' throws up precious secret] Citat: "..."It is very lucky that entire genomes were mapped, as this work is showing." He added: "I think other bits of 'junk' DNA will turn out not to be junk. I think this is the tip of the iceberg, and that there will be many more similar findings."..."</ref>
<ref>[http://www.sciencedaily.com/releases/2005/07/050710201806.htm 2005-07-12, Sciencedaily: Rodent Social Behavior Encoded In Junk DNA] Citat: "..."It was considered junk DNA because it didn't seem to have any function," noted Hammock..."</ref>
<ref>[http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=00045BB6-5D49-1150-902F83414B7F4945 October 2004, Scientific american: The Hidden Genetic Program of Complex Organisms] Citat: "...But an overlooked regulatory system based on RNA may hold the keys to development and evolution..."</ref>
<ref>[http://www.sciencedaily.com/releases/2007/04/070423185538.htm April 24, 2007, Sciencedaily: 'Junk' DNA Now Looks Like Powerful Regulator, Scientists Find] Citat: "...Many of those snippets were located in gene-free chromosomal expanses once described by geneticists as "gene deserts." These sections are, in fact, so clogged with useful DNA bits - including the ones Bejerano and his colleagues describe - that they've been renamed "regulatory jungles."...transposons that duplicate themselves and hop around the genome. "We used to think they were mostly messing things up. Here is a case where they are actually useful," Bejerano said..."Now we've shown that transposons may be a major vehicle for evolutionary novelty," he said...."</ref>
== Kilder/referencer ==
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[[Kategori:Liv]]
[[Kategori:Nukleinsyrer]]
[[ca:ADN escombraries]]
[[cs:Junk DNA]]
[[id:DNA sampah]]
[[ja:ジャンクDNA]]
[[ko:정크 (생물학)]]
[[ru:Мусорная ДНК]]
[[sv:Skräp-dna]]
[[tr:Kodlamayan DNA]]
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