An intergenic region is a stretch of
DNA
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
sequences located between
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
s.
Intergenic regions may contain functional elements and
junk DNA.
Properties and functions
Intergenic regions may contain a number of functional DNA sequences such as
promoters and regulatory elements,
enhancers,
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.
It is possible that these regions contain as of yet unidentified functional elements, such as non-coding genes or regulatory sequences.
This indeed occurs occasionally, but the amount of functional DNA discovered usually constitute only a tiny fraction of the overall amount of intergenic or intronic DNA.
Intergenic regions in different organisms
In humans, intergenic regions comprise about 50% of the
genome
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 genes, other functional regions of the genome such as ...
, whereas this number is much less in bacteria (15%) and yeast (30%).
As with most other non-coding DNA, the
GC-content
In molecular biology and genetics, GC-content (or guanine-cytosine content) is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine (G) or cytosine (C). This measure indicates the proportion of G and C bases out of ...
of intergenic regions vary considerably among species. For example in ''
Plasmodium falciparum
''Plasmodium falciparum'' is a Unicellular organism, unicellular protozoan parasite of humans and is the deadliest species of ''Plasmodium'' that causes malaria in humans. The parasite is transmitted through the bite of a female ''Anopheles'' mos ...
'', many intergenic regions have an AT content of 90%.
Molecular evolution of intergenic regions
Functional elements in intergenic regions will evolve slowly because their sequence is maintained by
negative selection. In species with very large genomes, a large percentage of intergenic regions is probably
junk DNA and it will evolve at the
neutral rate of evolution.
Junk DNA sequences are not maintained by
purifying selection but
gain-of-function mutations with deleterious fitness effects can occur.
inference and bioinformatics methods have shown that intergenic regions can—on geological timescales—transiently evolve into
open reading frame
In molecular biology, reading frames 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 reading frames ...
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.
See also
*
Exon
An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequence ...
*
Promoter (biology)
In genetics, a promoter is a sequence of DNA to which proteins bind to initiate transcription (genetics), transcription of a single RNA transcript from the DNA downstream of the promoter. The RNA transcript may encode a protein (mRNA), or can hav ...
*
ENCODE
*
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 regu ...
*
Repetitive DNA
*
Regulator gene
*
Whole genome sequencing
Whole genome sequencing (WGS), also known as full genome sequencing or just genome sequencing, is the process of determining the entirety of the DNA sequence of an organism's genome at a single time. This entails sequencing all of an organism's ...
References
{{reflist, 2
External links
ENCODE threads ExplorerCharacterization 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 review, peer-reviewed research from a variety of academic disciplines, mainly in science and t ...
DNA
Molecular biology