title: A single, recent origin of the accessory B chromosome of the grasshopper Eyprepocnemis plorans.
abstract: B chromosomes are dispensable chromosomes found in >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 cytogenetic 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.
authors.affiliation: Departamento de Genética, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain.
authors.forename: A Jesús
authors.initials: AJ
authors.lastname: Muñoz-Pajares
authors.forename: Laura
authors.initials: L
authors.lastname: Martínez-Rodríguez
authors.forename: María
authors.initials: M
authors.lastname: Teruel
authors.forename: Josefa
authors.initials: J
authors.lastname: Cabrero
authors.forename: Juan Pedro M
authors.initials: JP
authors.lastname: Camacho
authors.forename: Francisco
authors.initials: F
authors.lastname: Perfectti
mesh_terms: D000818:Animals; D002874:Chromosome Mapping; D059006:Chromosomes, Insect / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics; D004276:DNA, Satellite / Q000235:genetics*; D019143:Evolution, Molecular; D005819:Genetic Markers / Q000235:genetics*; D006110:Grasshoppers / Q000166:cytology* / Q000235:genetics*; D008297:Male; D012091:Repetitive Sequences, Nucleic Acid
chemical_list: D004275:DNA, Ribosomal; D004276:DNA, Satellite; D005819:Genetic Markers