Non-coding DNA: Difference between revisions

Revision as of 13:28, 26 March 2023

Revision as of 19:28, 21 April 2023

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The remainder of the genome (70% non-coding DNA) consists of promoters and regulatory sequences that are shorter than those in other plant species.<ref name = Ibarra-Laclette/> The genes contain introns but there are fewer of them and they are smaller than the introns in other plant genomes.<ref name = Ibarra-Laclette/> There are noncoding genes, including many copies of ribosomal RNA genes.<ref name = Lan/> The genome also contains telomere sequences and centromeres as expected.<ref name = Lan/> Much of the repetitive DNA seen in other eukaryotes has been deleted from the bladderwort genome since that lineage split from those of other plants. About 59% of the bladderwort genome consists of transposon-related sequences but since the genome is so much smaller than other genomes, this represents a considerable reduction in the amount of this DNA.<ref name = Lan/> The authors of the original 2013 article note that claims of additional functional elements in the non-coding DNA of animals do not seem to apply to plant genomes.<ref name = Ibarra-Laclette/>

According to a New York Times piece, during the evolution of this species, "... genetic junk that didn’tdidn't serve a purpose was expunged, and the necessary stuff was kept."<ref>{{cite news | vauthors = Klein J | title = Genetic Tidying Up Made Humped Bladderworts Into Carnivorous Plants | url = https://www.nytimes.com/2017/05/19/science/humped-bladderwort-carnivorous-plant-genome.html | work = New York Times | date = 19 May 2017 | access-date = May 30, 2022}}</ref> According to Victor Albert of the University of Buffalo, the plant is able to expunge its so-called junk DNA and "have a perfectly good multicellular plant with lots of different cells, organs, tissue types and flowers, and you can do it without the junk. Junk is not needed."<ref>{{ cite press release | vauthors = Hsu C, and Stolte D | date = May 13, 2013 | title = Carnivorous Plant Throws Out 'Junk' DNA | url = https://news.arizona.edu/story/carnivorous-plant-throws-out-junk-dna | ___location = Tucson, AZ, USA | publisher = University of Arizona | access-date = May 29, 2022}}</ref>

==Types of non-coding DNA sequences==

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===Centromeres===

{{Main|Centromere}}

[[File:Human karyotype with bands and sub-bands.png|thumb|Schematic [[karyotype|karyogram]] of a human, showing an overview of the [[human genome]] on [[G banding]], wherein non-coding DNA is present at the centromeres (shown as narrow segment of each chromosome), and also occurs to a greater extent in darker ([[GC-content|GC poor]]) regions.<ref name=Romiguier2017>{{cite journal | vauthors = Romiguier J, Roux C | title = Analytical Biases Associated with GC-Content in Molecular Evolution | journal = Frontiers in Genetics | volume = 8 | issue = | pages = 16 | year = 2017 | pmid = 28261263 | pmc = 5309256 | doi = 10.3389/fgene.2017.00016 | doi-access = free }} </ref><br>]]

Centromeres are the sites where spindle fibers attach to newly replicated chromosomes in order to segregate them into daughter cells when the cell divides. Each eukaryotic chromosome has a single functional centromere that's seen as a constricted region in a condensed metaphase chromosome. Centromeric DNA consists of a number of repetitive DNA sequences that often take up a significant fraction of the genome because each centromere can be millions of base pairs in length. In humans, for example, the sequences of all 24 centromeres have been determined<ref>{{ cite journal | vauthors = Altemose N, Logsdon GA, Bzikadze AV, Sidhwani P, Langley SA, Caldas GV, et al. | title = Complete genomic and epigenetic maps of human centromeres | journal = Science | volume = 376 | pages = 56 | date = 2021 | issue = 6588 | doi = 10.1126/science.abl4178| pmid = 35357911 | pmc = 9233505 | s2cid = 247853627 }}</ref> and they account for about 6% of the genome. However, it's unlikely that all of this noncoding DNA is essential since there is considerable variation in the total amount of centromeric DNA in different individuals.<ref>{{cite journal | vauthors = Miga KH | title = Centromeric satellite DNAs: hidden sequence variation in the human population | journal = Genes | volume = 10 | pages = 353 | date = 2019 | issue = 5 | doi = 10.3390/genes10050352| pmid = 31072070 | pmc = 6562703 | doi-access = free }}</ref> Centromeres are another example of functional noncoding DNA sequences that have been known for almost half a century and it's likely that they are more abundant than coding DNA.