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conserved sequence
In biology, conserved sequences are similar or identical sequences that occur within nucleic acid sequences (such as RNA and DNA sequences), protein sequences, protein structures or polymeric carbohydrates across species (orthologous sequences) or within different molecules produced by the same organism (paralogous sequences). In the case of cross species conservation, this indicates that a particular sequence may have been maintained by evolution despite speciation. The further back up the phylogenetic tree a particular conserved sequence may occur the more highly conserved it is said to be. Since sequence information is normally transmitted from parents to progeny by genes, a conserved sequence implies that there is a conserved gene.
It is widely believed that mutation in a "highly conserved" region leads to a non-viable life form, or a form that is eliminated through natural selection.
==Nucleic acid and protein sequences==
Highly conserved DNA sequences are thought to have functional value. The role for many of these highly conserved non-coding DNA sequences is not understood. Ultra-conserved elements or sequences (UCEs or UCRs, ''ultra-conserved regions'') that share 100% identity among human, mouse and rat were first described by Bejerano and colleagues in 2004. One recent study that eliminated four highly conserved non-coding DNA sequences in mice yielded viable mice with no significant phenotypic differences; the authors described their findings as "unexpected". Many regions of the DNA, including highly conserved DNA sequences, consist of repeated sequence (DNA) elements. One possible explanation of the null hypothesis above is that removal of only one or a subset of a repeated sequence could theoretically preserve phenotypic functioning on the assumption that one such sequence is sufficient and the repetitions are superfluous to essential life processes; it was not specified in the paper whether the eliminated sequences were repeated sequences. Although most of the conserved sequences' biological function is still unknown, few conserved sequences derived transcripts showed that their expression is deregulated in human cancer tissues.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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