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Genes take up about 30% of the pufferfish genome and the coding DNA is about 10%. (Non-coding DNA = 90%.) The reduced size of the pufferfish genome is due to a reduction in the length of introns and less repetitive DNA. [8] [9] Utricularia gibba, a bladderwort plant, has a very small nuclear genome (100.7 Mb) compared to most plants.
Junk DNA (non-functional DNA) is a DNA sequence that has no known biological function. [ 1 ] [ 2 ] Most organisms have some junk DNA in their genomes —mostly, pseudogenes and fragments of transposons and viruses—but it is possible that some organisms have substantial amounts of junk DNA.
A conserved non-coding sequence (CNS) is a DNA sequence of noncoding DNA that is evolutionarily conserved. These sequences are of interest for their potential to regulate gene production. [1] CNSs in plants [2] and animals [1] are highly associated with transcription factor binding sites and other cis-acting regulatory elements.
For example, only about 1.5% of the human genome consists of protein-coding exons, with over 50% of human DNA consisting of non-coding repetitive sequences. [98] The reasons for the presence of so much noncoding DNA in eukaryotic genomes and the extraordinary differences in genome size , or C-value , among species, represent a long-standing ...
The total amount of coding DNA is about 1-2% of the genome. [18] [16] Many people divide the genome into coding and non-coding DNA based on the idea that coding DNA is the most important functional component of the genome. About 98-99% of the human genome is non-coding DNA.
In the late 2000s, genome annotation shifted its attention towards identifying non-coding regions in DNA, which was achieved thanks to the appearance of methods to analyze transcription factor binding sites, DNA methylation sites, chromatin structure, and other RNA and regulatory region analysis techniques.
In 2005 the landscape of the mammalian genome was described as numerous 'foci' of transcription that are separated by long stretches of intergenic space. [9] While some long ncRNAs are located within the intergenic stretches, the majority are overlapping sense and antisense transcripts that often include protein-coding genes, [23] giving rise to a complex hierarchy of overlapping isoforms. [24]
Reading frames in the DNA sequence of a region of the human mitochondrial genome coding for the genes MT-ATP8 and MT-ATP6 (in black: positions 8,525 to 8,580 in the sequence accession NC_012920 [31]). There are three possible reading frames in the 5' → 3' forward direction, starting on the first (+1), second (+2) and third position (+3).