The random versus fragile breakage models of chromosome evolution: a matter of resolution |
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Authors: | Thomas S Becker Boris Lenhard |
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Institution: | (1) Sars Centre, University of Bergen, Bergen, Norway;(2) Computational Biology Unit, University of Bergen, Bergen, Norway |
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Abstract: | Conserved synteny––the sharing of at least one orthologous gene by a pair of chromosomes from two species––can, in the strictest
sense, be viewed as sequence conservation between chromosomes of two related species, irrespective of whether coding or non-coding
sequence is examined. The recent sequencing of multiple vertebrate genomes indicates that certain chromosomal segments of
considerable size are conserved in gene order as well as underlying non-coding sequence across all vertebrates. Some of these
segments lost genes or non-coding sequence and/or underwent breakage only in teleost genomes, presumably because evolutionary
pressure acting on these regions to remain intact were relaxed after an additional round of whole genome duplication. Random
reporter insertions into zebrafish chromosomes combined with computational genome-wide analysis indicate that large chromosomal
areas of multiple genes contain long-range regulatory elements, which act on their target genes from several gene distances
away. In addition, computational breakpoint analyses suggest that recurrent evolutionary breaks are found in “fragile regions”
or “hotspots”, outside of the conserved blocks of synteny. These findings cannot be accommodated by the random breakage model
and suggest that this view of genome and chromosomal evolution requires substantial reassessment. |
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Keywords: | Genome evolution Synteny blocks Genomic regulatory blocks Bystander gene |
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