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

retrotransposon Retrotransposons (also called Class I transposable elements or transposons via RNA intermediates) are a type of genetic component that copy and paste themselves into different genomic locations ( transposon) by converting RNA back into DNA throu ...

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 Gene conversion is the process by which one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion event. Gene conversion can be either allelic, meaning that one allele of the same gene replaces a ...

during

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...

Intrachromosomal and interchromosomal gene conversion

Gene conversion Gene conversion is the process by which one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion event. Gene conversion can be either allelic, meaning that one allele of the same gene replaces a ...

acts on DNA

sequence homology Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a ...

as its substrate. There is no requirement that the sequence homologies lie at the

allelic An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...

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 A gene family is a set of several similar genes, formed by duplication of a single original gene, and generally with similar biochemical functions. One such family are the genes for human hemoglobin subunits; the ten genes are in two clusters on ...

situated on the same chromosome. 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

Repetitive sequences play the role of uncoupling the gene conversion network, thereby allowing new genes to evolve. The shorter Alu or

SINE In mathematics, sine and cosine are trigonometric functions of an angle. The sine and cosine of an acute angle are defined in the context of a right triangle: for the specified angle, its sine is the ratio of the length of the side that is opp ...

repetitive DNA are specialized for uncoupling intrachromosomal gene conversion while the longer

LINE Line most often refers to: * Line (geometry), object with zero thickness and curvature that stretches to infinity * Telephone line, a single-user circuit on a telephone communication system Line, lines, The Line, or LINE may also refer to: Art ...

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 Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

. 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 Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution withi ...

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. Gene pool3

References

* {{Self-replicating organic structures Mobile genetic elements Repetitive DNA sequences

Intrachromosomal and interchromosomal gene conversion

Role of interspersed repetitive DNA

Interspersed DNA elements catalyze the evolution of new genes

See also

References