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An intergenic region is a stretch of DNA sequences located between
ENCODE threads Explorer
Characterization of intergenic regions and gene definition.
An intergenic region is a stretch of DNA sequences located between gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
s. Intergenic regions may contain functional elements and junk DNA. ''Inter''genic regions should not be confused with ''intra''genic regions (or introns
An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of the cistron .e., gene ...
), which are non-coding regions that are found ''within'' genes, especially within the genes of eukaryotic
Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...
organisms.
Properties and functions
Intergenic regions may contain a number of functional DNA sequences such as promoters and regulatory elements,enhancers
In genetics, an enhancer is a short (50–1500 bp) region of DNA that can be bound by proteins ( activators) to increase the likelihood that transcription of a particular gene will occur. These proteins are usually referred to as transcriptio ...
, spacers, and (in eukaryotes) centromeres. They may also contain origins of replication, scaffold attachment regions, and transposons and viruses. Non-functional DNA elements such as pseudogenes and repetitive DNA, both of which are types of junk DNA, can also be found in intergenic regions—although they may also be located within genes in introns.
As all scientific knowledge is ultimately tentative—and in principle subject to revision given better evidence—it is possible some well-characterized intergenic regions (but also intra-genic regions like introns
An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of the cistron .e., gene ...
) may hypothetically contain as yet unidentified functional elements, such as non-coding RNA genes or regulatory sequences. Such discoveries occur from time to time, but the amount of functional DNA discovered usually constitute only a tiny fraction of the overall amount of intergenic/intronic DNA.
Intergenic regions in different organisms
In humans, intergenic regions comprise about 50% of thegenome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
, whereas this number is much less in bacteria (15%) and yeast (30%).
As with most other non-coding DNA, the GC-content of intergenic regions vary considerably among species. For example in '' Plasmodium falciparum'', many intergenic regions have an AT content of 90%.
Molecular evolution of Intergenic regions
As intergenic regions are a subset of the noncoding genome, the majority is thought to evolve at close to theneutral
Neutral or neutrality may refer to:
Mathematics and natural science Biology
* Neutral organisms, in ecology, those that obey the unified neutral theory of biodiversity
Chemistry and physics
* Neutralization (chemistry), a chemical reaction in ...
rate of mutation in species with small effective population sizes. Because a large fraction of intergenic regions in such species probably consist of junk DNA
Non-coding DNA (ncDNA) sequences are components of an organism's DNA that do not encode protein sequences. Some non-coding DNA is transcribed into functional non-coding RNA molecules (e.g. transfer RNA, microRNA, piRNA, ribosomal RNA, and regula ...
(thereby explaining the overall lack of sequence conservation
In evolutionary biology, conserved sequences are identical or similar sequences in nucleic acids ( DNA and RNA) or proteins across species ( orthologous sequences), or within a genome ( paralogous sequences), or between donor and receptor taxa ...
in this fraction), these intergenic regions are generally not maintained by natural selection and thus only experience negative selection when, by chance, gain-of-function
Gain-of-function research (GoF research or GoFR) is medical research that genetically alters an organism in a way that may enhance the biological functions of gene products. This may include an altered pathogenesis, transmissibility, or host ...
mutations with deleterious fitness effects occur.
Phylostratigraphic inference and bioinformatics methods have shown that intergenic regions can—on geological timescales—transiently evolve into open reading frame
In molecular biology, open reading frames (ORFs) are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible readin ...
sequences that mimic those of protein coding genes, and can therefore lead to the evolution of novel protein-coding genes in a process known as de novo gene birth
''De novo'' gene birth is the process by which new genes evolve from DNA sequences that were ancestrally non-genic. '' De novo'' genes represent a subset of novel genes, and may be protein-coding or instead act as RNA genes. The processes tha ...
.
See also
* Exon * Promoter (biology) *ENCODE
The Encyclopedia of DNA Elements (ENCODE) is a public research project which aims to identify functional elements in the human genome.
ENCODE also supports further biomedical research by "generating community resources of genomics data, software ...
* Heterochromatin
* Noncoding DNA
Non-coding DNA (ncDNA) sequences are components of an organism's DNA that do not encode protein sequences. Some non-coding DNA is transcribed into functional non-coding RNA molecules (e.g. transfer RNA, microRNA, piRNA, ribosomal RNA, and r ...
* Repetitive DNA
Repeated sequences (also known as repetitive elements, repeating units or repeats) are short or long patterns of nucleic acids (DNA or RNA) that occur in multiple copies throughout the genome. In many organisms, a significant fraction of the geno ...
* Regulator gene
A regulator gene, regulator, or regulatory gene is a gene involved in controlling the expression of one or more other genes. Regulatory sequences, which encode regulatory genes, are often at the five prime end (5') to the start site of transcrip ...
* Whole genome sequencing
Whole genome sequencing (WGS), also known as full genome sequencing, complete genome sequencing, or entire genome sequencing, is the process of determining the entirety, or nearly the entirety, of the DNA sequence of an organism's genome at a ...
References
{{reflist, 2External links
ENCODE threads Explorer
Characterization of intergenic regions and gene definition.
Nature (journal)
''Nature'' is a British weekly scientific journal founded and based in London, England. As a multidisciplinary publication, ''Nature'' features peer-reviewed research from a variety of academic disciplines, mainly in science and technology. ...
DNA
Molecular biology