Genomic Organization Wiki
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Genomic organization
Genome sizes and corresponding composition of six major model
organisms as pie charts. The increase in genome size correlates
with the vast expansion of noncoding (i.e., intronic, intergenic,
and interspersed repeat sequences) and repeat DNA (e.g., satel-
lite, LINEs, Short interspersed nuclear element (SINEs), DNA
(Alu sequence), in red) sequences in more complex muiticellu-
lar organisms. This expansion is accompanied by an increase
in the number of epigenetic mechanisms (particularly repressive)
that regulate the genome. Expansion of the genome also cor-
relates with an increase in size and complexity of transcription
units, with the exception of plants. P = Promoter DNA element.
The hereditary material i.e. DNA(deoxyribonuclic acid)
of an organism is composed of an array of arrangement of
four nucleotides in a specific pattern. These nucleotides
present an inherent information as a function of their or-
der. The genome of all organisms (except some viruses
and prions) is composed of one to multiple number of
these DNA molecules. To draw an analogy it can be said
that genome when seen from viewpoint of sequences of
these nucleotides alone, is like a book which doesn't have
any chapters or paragraphs or even sentences. Hence,
these nucleotides conceal a layer of unapparent informa-
tion. Genomic organisation of an organism is this back-
ground layer of information which unassumingly providesmultiple layer of information to structure genome from
the array of nucleotide sequences.
1 Description
Organisms have a vast array of ways in which their re-
spective genomes are organized. A comparison of the ge-
nomic organization of six major model organisms shows
size expansion with the increase of complexity of the or-
ganism. There is a more than 300-fold difference be-
tween the genome sizes of yeast and mammals, but only a
modest 4- to 5-fold increase in overall gene number (see
the figure on the right). However, the ratio of coding to
noncoding and repetitive sequences is indicative of thecomplexity of the genome: The largely “open” genomes
of unicellular fungi have relatively little noncoding DNA
compared with the highly heterochromatic genomes of
multicellular organisms.
In particular, mammals have accumulated considerable
repetitive elements and noncoding regions, which ac-
count for the majority of their DNA sequences (52%
non-coding and 44% repetitive DNA).[1][2] Only 1.2% of
the mammalian genome thus encodes for protein func-
tion. This massive expansion of repetitive and noncod-
ing sequences in multicellular organisms is most likely
due to the incorporation of invasive elements, such asDNA transposons, retrotransposons, and other repetitive
elements.[3] The expansion of repetitive elements (such
as Alu sequences) has even infiltrated the transcriptional
units of the mammalian genome. This results in tran-
scription units that are frequently much larger (30-200
kb), commonly containing multiple promoters and DNA
repeats within untranslated introns.
The vast expansion of the genome with noncoding and
repetitive DNA in higher eukaryotes implies more exten-
sive epigenetic silencing mechanisms. Studies of the ge-
nomic organization is thought to be the future of genomic
medicine, which will provide the opportunity for person-alized prognoses in clinics.[4]
2 See also
• Genome Comparison
• Genome project
•
List of sequenced eukaryotic genomes
• Molecular evolution
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https://en.wikipedia.org/wiki/Molecular_evolutionhttps://en.wikipedia.org/wiki/List_of_sequenced_eukaryotic_genomeshttps://en.wikipedia.org/wiki/Genome_projecthttps://en.wikipedia.org/wiki/Genome_Comparisonhttps://en.wikipedia.org/wiki/Prognosishttps://en.wikipedia.org/wiki/Medicinehttps://en.wikipedia.org/wiki/Epigeneticshttps://en.wikipedia.org/wiki/Eukaryotehttps://en.wikipedia.org/wiki/Intronhttps://en.wikipedia.org/wiki/Transcription_(genetics)https://en.wikipedia.org/wiki/Alu_sequencehttps://en.wikipedia.org/wiki/Retrotransposonhttps://en.wikipedia.org/wiki/Transposonhttps://en.wikipedia.org/wiki/Proteinhttps://en.wikipedia.org/wiki/Repetitive_DNAhttps://en.wikipedia.org/wiki/Multicellularhttps://en.wikipedia.org/wiki/Heterochromatinhttps://en.wikipedia.org/wiki/DNAhttps://en.wikipedia.org/wiki/Fungihttps://en.wikipedia.org/wiki/Unicellularhttps://en.wikipedia.org/wiki/Genehttps://en.wikipedia.org/wiki/Mammalhttps://en.wikipedia.org/wiki/Yeasthttps://en.wikipedia.org/wiki/Complexityhttps://en.wikipedia.org/wiki/Genomehttps://en.wikipedia.org/wiki/Organismhttps://en.wikipedia.org/wiki/Promoter_(biology)https://en.wikipedia.org/wiki/Epigenetichttps://en.wikipedia.org/wiki/Alu_sequencehttps://en.wikipedia.org/wiki/Short_interspersed_nuclear_elementhttps://en.wikipedia.org/wiki/DNAhttps://en.wikipedia.org/wiki/Genome
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2 3 REFERENCES
3 References
[1] Venter G, et al., The Sequence of the Human Genome
Science (2001) 291. pp1304-51
[2] R. A. Harris et al., Human-Specific Changes of Genome
Structure Detected by Genomic Triangulation Science(2007) 316.5822, pp. 235-7
[3] Haig H. Kazazian, Jr. Mobile Elements: Drivers of
Genome Evolution Science, Mar 2004; 303: 1626-32
[4] West M., et al., Embracing the complexity of ge-
nomic data for personalized medicine Genome Res.
(2006)16:559-66
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