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

1

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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