Abstract
BackgroundSupernumerary B chromosomes occur in addition to standard karyotype and have been described in about 15% of eukaryotes, being the repetitive DNAs the major component of these chromosomes, including in some cases the presence of multigene families. To advance in the understanding of chromosomal organization of multigene families and B chromosome structure and evolution, the distribution of rRNA and H3 histone genes were analyzed in the standard karyotype and B chromosome of three populations of the grasshopper Rhammatocerus brasiliensis.ResultsThe location of major rDNA was coincident with the previous analysis for this species. On the other hand, the 5S rDNA mapped in almost all chromosomes of the standard complement (except in the pair 11) and in the B chromosome, showing a distinct result from other populations previously analyzed. Besides the spreading of 5S rDNA in the genome of R. brasiliensis it was also observed multiple sites for H3 histone genes, being located in the same chromosomal regions of 5S rDNAs, including the presence of the H3 gene in the B chromosome.ConclusionsDue to the intense spreading of 5S rRNA and H3 histone genes in the genome of R. brasiliensis, their chromosomal distribution was not informative in the clarification of the origin of B elements. Our results indicate a linked organization for the 5S rRNA and H3 histone multigene families investigated in R. brasiliensis, reinforcing previous data concerning the association of both genes in some insect groups. The present findings contribute to understanding the organization/evolution of multigene families in the insect genomes.
Highlights
Supernumerary B chromosomes occur in addition to standard karyotype and have been described in about 15% of eukaryotes, being the repetitive DNAs the major component of these chromosomes, including in some cases the presence of multigene families
In eukaryotes the transcribing sequences for ribosomal RNAs are organized in two multigenic families tandemly arrayed in the genomes
Concerning multigene families in Acrididae the major rDNA was mapped in 53 species, the histone genes were located in chromosomes of 39 species and the 5S rDNA distribution was described in about 30 species [4,5,6,7,9,10]
Summary
Supernumerary B chromosomes occur in addition to standard karyotype and have been described in about 15% of eukaryotes, being the repetitive DNAs the major component of these chromosomes, including in some cases the presence of multigene families. Concerning multigene families in Acrididae the major rDNA was mapped in 53 species, the histone genes were located in chromosomes of 39 species and the 5S rDNA distribution was described in about 30 species [4,5,6,7,9,10]. The mapping of these sequences together with the satDNA has been an important tool for understanding several aspects of the chromosome biology of acridid grasshopers [4,9,10]. In this group variability for B chromosomes related to heterochromatin patterns, satellite DNAs organization and multigene families has been reported [4,9,10,12,13,14]
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