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Jueves 13/01/2011
Origen único y reciente de los cromosomas B de E. plorans
MS aceptado en Genetics
B chromosomes are dispensable chromosomes found in more than 2000 eukaryotic species, usually behaving as genomic parasite ...
MS aceptado en Genetics
B chromosomes are dispensable chromosomes found in more than 2000 eukaryotic species, usually behaving as genomic parasites. Most B chromosomes seem to be made up of the same kind of DNA sequences present in the A-chromosomes. This sequence similarity makes it difficult to obtain specific molecular probes that may permit B-presence diagnosis without cytogenetical analysis. We have developed a Sequence Characterized Amplified Region (SCAR) marker for B chromosomes in the grasshopper Eyprepocnemis plorans, which specifically amplifies a 1510 bp DNA fragment exclusively in B-carrying individuals. Fluorescent in situ hybridization and Fiber FISH analyses showed that this marker is a tandemly repeated DNA sequence closely intermingled with 45S rDNA. PCR reactions showed the presence of SCAR-like sequences in the A chromosomes, but in two separate fragments, supporting the intraspecific origin of B chromosomes in this species. SCAR marker DNA sequence showed to be identical in B chromosome variants from several localities from Spain and Morocco, and it was very similar to those found in B chromosome variants from Greece and Armenia. This strongly suggests that this sequence was already present in the ancestral B chromosome of this species. In addition, the scarce sequence variation observed among several B variants from very distant populations suggests either, a functional constraint or, more likely, a recent and unique origin for B chromosomes in this species.