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Interspersed repetitive DNA is found in all eukaryotic genomes. They differ from tandem repeat DNA in that rather than the repeat sequences coming right after one another, they are dispersed throughout the genome and nonadjacent. The sequence that repeats can vary depending on the type of organism, and many other factors. Certain classes of interspersed repeat sequences propagate themselves by RNA mediated transposition; they have been called retrotransposons, and they constitute 25–40% of most mammalian genomes. Some types of interspersed repetitive DNA elements allow new genes to evolve by uncoupling similar DNA sequences from gene conversion during meiosis.^[1]

Intrachromosomal and interchromosomal gene conversion

Gene conversion acts on DNA sequence homology as its substrate. There is no requirement that the sequence homologies lie at the allelic positions on their respective chromosomes or even that the homologies lie on different chromosomes. Gene conversion events can occur between different members of a gene family situated on the same chromosome.^[2] When this happens, it is called intrachromosomal gene conversion as distinguished from interchromosomal gene conversion. The effect of homogenizing DNA sequences is the same.

Role of interspersed repetitive DNA

Repetitive sequences play the role of uncoupling the gene conversion network, thereby allowing new genes to evolve. The shorter Alu or SINE repetitive DNA are specialized for uncoupling intrachromosomal gene conversion while the longer LINE repetitive DNA are specialized for uncoupling interchromosomal gene conversion. In both cases, the interspersed repeats block gene conversion by inserting regions of non-homology within otherwise similar DNA sequences. The homogenizing forces linking DNA sequences are thereby broken and the DNA sequences are free to evolve independently. This leads to the creation of new genes and new species during evolution.^[3] By breaking the links that would otherwise overwrite novel DNA sequence variations, interspersed repeats catalyse evolution, allowing the new genes and new species to develop.

Interspersed DNA elements catalyze the evolution of new genes

DNA sequences are linked together in a gene pool by gene conversion events. Insertion of an interspersed DNA element breaks this linkage, allowing independent evolution of a new gene. The interspersed repeat is an isolating mechanism enabling new genes to evolve without interference from the progenitor gene. Because insertion of an interspersed repeat is a saltatory event the evolution of the new gene will also be saltatory. Because speciation ultimately depends on the creation of new genes, this naturally causes punctuated equilibria. Interspersed repeats are thus responsible for punctuated evolution and rapid modes of evolution.

References

^ Schimenti JC, Duncan CH (February 1984). "Ruminant globin gene structures suggest an evolutionary role for Alu-type repeats". Nucleic Acids Res. 12 (3): 1641–55. doi:10.1093/nar/12.3.1641. PMC 318605. PMID 6322113.
^ Hess JF, Fox M, Schmid C, Shen CK (October 1983). "Molecular evolution of the human adult alpha-globin-like gene region: insertion and deletion of Alu family repeats and non-Alu DNA sequences". Proc. Natl. Acad. Sci. U.S.A. 80 (19): 5970–4. Bibcode:1983PNAS...80.5970H. doi:10.1073/pnas.80.19.5970. PMC 390199. PMID 6310609.
^ Brunner AM, Schimenti JC, Duncan CH (September 1986). "Dual evolutionary modes in the bovine globin locus". Biochemistry. 25 (18): 5028–35. doi:10.1021/bi00366a009. PMID 3768329.

Interspersed+Repetitive+Sequences at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

[1] Schimenti JC, Duncan CH (February 1984). "Ruminant globin gene structures suggest an evolutionary role for Alu-type repeats". Nucleic Acids Res. 12 (3): 1641–55. doi:10.1093/nar/12.3.1641. PMC 318605. PMID 6322113.

[2] Hess JF, Fox M, Schmid C, Shen CK (October 1983). "Molecular evolution of the human adult alpha-globin-like gene region: insertion and deletion of Alu family repeats and non-Alu DNA sequences". Proc. Natl. Acad. Sci. U.S.A. 80 (19): 5970–4. Bibcode:1983PNAS...80.5970H. doi:10.1073/pnas.80.19.5970. PMC 390199. PMID 6310609.

[3] Brunner AM, Schimenti JC, Duncan CH (September 1986). "Dual evolutionary modes in the bovine globin locus". Biochemistry. 25 (18): 5028–35. doi:10.1021/bi00366a009. PMID 3768329.

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-'''Interspersed repetitive DNA''' is found in all eukaryotic [[genomes]]. Certain classes of these sequences propagate themselves by RNA mediated transposition, and they have been called [[retrotransposon]]s. Interspersed repetitive DNA elements allow new genes to evolve. They do this by uncoupling similar DNA sequences from [[gene conversion]] during [[meiosis]]<ref> {{cite journal |author=Schimenti JC, Duncan CH |title=Ruminant globin gene structures suggest an evolutionary role for Alu-type repeats |journal=Nucleic Acids Res. |volume=12 |issue=3 |pages=1641–55 |year=1984 |month=February |pmid=6322113 |pmc=318605 |doi= 10.1093/nar/12.3.1641|url=http://nar.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=6322113}}</ref>. The recombinational events of meiosis create heteroduplexes composed of strands from each parental chromosome. These heteroduplexes lead to mismatch repair. The net result is the homogenization and elimination of sequence differences during meiosis. Gene conversion can be viewed as the force acting to create sequence identity within the [[gene pool]] of a [[species]]. This is a cohesive force acting to match up DNA sequences of individual organisms that comprise a [[species]]. In effect the gene conversion causes the DNA sequences to ''clump together'' within a species and by doing so creates the natural boundaries between [[species]]. The [[gene pool]] of a [[species]] consists of DNA sequences linked in a network by [[gene conversion]] events.
+'''Interspersed repetitive DNA''' is found in all eukaryotic [[genomes]]. They differ from [[tandem repeat]] DNA in that rather than the repeat sequences coming right after one another, they are dispersed throughout the genome and nonadjacent. The sequence that repeats can vary depending on the type of organism, and many other factors. Certain classes of interspersed repeat sequences propagate themselves by RNA mediated [[Transposable element|transposition]]; they have been called [[retrotransposon]]s, and they constitute 25–40% of most mammalian genomes. Some types of interspersed repetitive DNA elements allow new genes to evolve by uncoupling similar DNA sequences from [[gene conversion]] during [[meiosis]].<ref>{{cite journal |vauthors=Schimenti JC, Duncan CH |title=Ruminant globin gene structures suggest an evolutionary role for Alu-type repeats |journal=Nucleic Acids Res. |volume=12 |issue=3 |pages=1641–55 |date=February 1984 |pmid=6322113 |pmc=318605 |doi= 10.1093/nar/12.3.1641|url=}}</ref>
 ==Intrachromosomal and interchromosomal gene conversion==
-Gene conversion acts on DNA sequence homology as its substrate. There is no requirement that the sequence homologies lie at the [[allele|allelic]] positions on their respective chromosomes or even that the homologies lie on different chromosomes. Gene conversion events can occur between different members of a [[gene family]] situated on the same chromosome<ref>{{cite journal |author=Hess JF, Fox M, Schmid C, Shen CK |title=Molecular evolution of the human adult alpha-globin-like gene region: insertion and deletion of Alu family repeats and non-Alu DNA sequences |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=80 |issue=19 |pages=5970–4 |year=1983 |month=October |pmid=6310609 |pmc=390199 |doi= 10.1073/pnas.80.19.5970|url=http://www.pnas.org/cgi/content/abstract/80/19/5970}}</ref>. When this happens, it is called intrachromosomal gene conversion as distinguished from interchromosomal gene conversion. The effect of homogenizing DNA sequences is the same.<br />
+[[Gene conversion]] acts on DNA [[sequence homology]] as its substrate. There is no requirement that the sequence homologies lie at the [[allele|allelic]] positions on their respective chromosomes or even that the homologies lie on different chromosomes. Gene conversion events can occur between different members of a [[gene family]] situated on the same chromosome.<ref>{{cite journal |vauthors=Hess JF, Fox M, Schmid C, Shen CK |title=Molecular evolution of the human adult alpha-globin-like gene region: insertion and deletion of Alu family repeats and non-Alu DNA sequences |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=80 |issue=19 |pages=5970–4 |date=October 1983 |pmid=6310609 |pmc=390199 |doi= 10.1073/pnas.80.19.5970|bibcode=1983PNAS...80.5970H |doi-access=free }}</ref> When this happens, it is called ''intra''chromosomal gene conversion as distinguished from ''inter''chromosomal gene conversion. The effect of homogenizing DNA sequences is the same.
-==Role of Interspersed Repetitive DNA==
+==Role of interspersed repetitive DNA==
-Repetitive sequences play the role of uncoupling the gene conversion network, thereby allowing new genes to evolve. The shorter [[Alu sequence|Alu]] or [[SINE]] repetitive DNA are specialized for uncoupling intrachromosomal gene conversion while the longer LINE repetitive DNA are specialized for uncoupling interchromosomal gene conversion. In both cases, the interspersed repeats block gene conversion by inserting regions of non-homology within otherwise similar DNA sequences. The homogenizing forces linking DNA sequences are thereby broken and the DNA sequences are free to evolve independently. This leads to the creation of new genes and new species during [[evolution]]<ref>{{cite journal |author=Brunner AM, Schimenti JC, Duncan CH |title=Dual evolutionary modes in the bovine globin locus |journal=Biochemistry |volume=25 |issue=18 |pages=5028–35 |year=1986 |month=September |pmid=3768329 |doi= 10.1021/bi00366a009|url=http://pubs.acs.org/doi/abs/10.1021/bi00366a009}}</ref>. By breaking the links that would otherwise overwrite novel DNA sequence variations, interspersed repeats catalyse evolution, allowing the new genes and new species to develop.
+Repetitive sequences play the role of uncoupling the gene conversion network, thereby allowing new genes to evolve. The shorter [[Alu sequence|Alu]] or [[Short interspersed element|SINE]] repetitive DNA are specialized for uncoupling intrachromosomal gene conversion while the longer [[Long interspersed nuclear element|LINE]] repetitive DNA are specialized for uncoupling interchromosomal gene conversion. In both cases, the interspersed repeats block gene conversion by inserting regions of non-homology within otherwise similar DNA sequences. The homogenizing forces linking DNA sequences are thereby broken and the DNA sequences are free to evolve independently. This leads to the creation of new genes and new species during [[evolution]].<ref>{{cite journal |vauthors=Brunner AM, Schimenti JC, Duncan CH |title=Dual evolutionary modes in the bovine globin locus |journal=Biochemistry |volume=25 |issue=18 |pages=5028–35 |date=September 1986 |pmid=3768329 |doi= 10.1021/bi00366a009}}</ref> By breaking the links that would otherwise overwrite novel DNA sequence variations, interspersed repeats catalyse evolution, allowing the new genes and new species to develop.
-[[Image:Rep_dna_gene_conversion.JPG|Mechanism of Repetitive DNA Sequences in blocking gene conversion]]
+[[Image:Rep dna gene conversion.JPG|Mechanism of Repetitive DNA Sequences in blocking gene conversion]]
 ==Interspersed DNA elements catalyze the evolution of new genes==
 DNA sequences are linked together in a gene pool by gene conversion events. Insertion of an interspersed DNA element breaks this linkage, allowing independent evolution of a new gene. The interspersed repeat is an [[Reproductive isolation|isolating mechanism]] enabling new genes to evolve without interference from the progenitor gene. Because insertion of an interspersed repeat is a saltatory event the evolution of the new gene will also be saltatory. Because [[speciation]] ultimately depends on the creation of new genes, this naturally causes [[punctuated equilibrium|punctuated equilibria]]. Interspersed repeats are thus responsible for punctuated evolution and [[rapid modes of evolution]].
-[[File:Gene pool2.JPG|Insertion of interspersed DNA unlinking a gene pool]]
+[[File:Gene pool3.JPG|Insertion of interspersed DNA unlinking a gene pool]]
 ==See also==
@@ Line 17: / Line 18: @@
 *[[Genomic organization]]
 *[[L1Base]]
-==External links==
-* http://www.repetitive-dna.org
 ==References==
@@ Line 27: / Line 25: @@
 {{Repeated sequence}}
+{{Self-replicating organic structures}}
 [[Category:Mobile genetic elements]]
 [[Category:Repetitive DNA sequences]]