Abstract
B chromosomes occur in approximately 15% of eukaryotes and are usually heterochromatic and rich in repetitive DNAs. Here we describe characteristics of a B chromosome in the grasshopper Eumastusia koebelei koebelei (Rehn, 1909) through classical cytogenetic methods and mapping of some repetitive DNAs, including multigene families, telomeric repeats and a DNA fraction enriched with repetitive DNAs obtained from DOP-PCR. Eumastusia koebelei koebelei presented 2n=23, X0 and, in one individual, two copies of the same variant of a B chromosome were noticed, which are associated during meiosis. The C-positive blocks were located in the pericentromeric regions of the standard complement and along the entire length of the B chromosomes. Some G+C-rich heterochromatic blocks were noticed, including conspicuous blocks in the B chromosomes. The mapping of 18S rDNA and U2 snDNA revealed only autosomal clusters, and the telomeric probe hybridized in terminal regions. Finally, the DOP-PCR probe obtained from an individual without a B chromosome revealed signals in the heterochromatic regions, including the entire length of the B chromosome. The possible intraspecific origin of the B chromosomes, due to the shared pool of repetitive DNAs between the A and B chromosomes and the possible consequences of their association are discussed.
Highlights
The grasshoppers of the subfamily Leptysminae (Orthoptera, Acrididae) are divided into two tribes, Leptysmini and Tetrataeniini, comprising 75 species distributed exclusively in the Neotropical region (Amedegnato 1974, Carbonell 1977, Roberts and Carbonell 1982)
The analyses were performed through conventional and differential chromosome staining and through fluorescent in situ hybridization (FISH) using distinct probes, such as 18S ribosomal DNA (rDNA), the TTAGG telomeric motif, U2 snDNA and a repetitive DNA fraction obtained by degenerate oligonucleotide-primed polymerase chain reaction (PCR) (DOP-PCR)
The 18S ribosomal DNA sequence and the U2 snDNA were obtained through polymerase chain reaction (PCR) from the genomes of Dichotomius semisquamosus (Curtis, 1845) (Coleoptera, Scarabaeidae) and Abracris flavolineata (De Geer, 1773) (Orthoptera, Acrididae), respectively, using primers described by Cabralde-Mello et al (2010) and Bueno et al (2013)
Summary
The grasshoppers of the subfamily Leptysminae (Orthoptera, Acrididae) are divided into two tribes, Leptysmini and Tetrataeniini, comprising 75 species distributed exclusively in the Neotropical region (Amedegnato 1974, Carbonell 1977, Roberts and Carbonell 1982). The analyses were performed through conventional and differential chromosome staining and through fluorescent in situ hybridization (FISH) using distinct probes, such as 18S rDNA, the TTAGG telomeric motif, U2 snDNA and a repetitive DNA fraction obtained by degenerate oligonucleotide-primed PCR (DOP-PCR).
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