The B chromosomes of the African cichlid fish Haplochromis obliquidens harbour 18S rRNA gene copies

Abstract

BackgroundDiverse plant and animal species have B chromosomes, also known as accessory, extra or supernumerary chromosomes. Despite being widely distributed among different taxa, the genomic nature and genetic behavior of B chromosomes are still poorly understood.ResultsIn this study we describe the occurrence of B chromosomes in the African cichlid fish Haplochromis obliquidens. One or two large B chromosome(s) occurring in 39.6% of the analyzed individuals (both male and female) were identified. To better characterize the karyotype and assess the nature of the B chromosomes, fluorescence in situ hybridization (FISH) was performed using probes for telomeric DNA repeats, 18S and 5S rRNA genes, SATA centromeric satellites, and bacterial artificial chromosomes (BACs) enriched in repeated DNA sequences. The B chromosomes are enriched in repeated DNAs, especially non-active 18S rRNA gene-like sequences.ConclusionOur results suggest that the B chromosome could have originated from rDNA bearing subtelo/acrocentric A chromosomes through formation of an isochromosome, or by accumulation of repeated DNAs and rRNA gene-like sequences in a small proto-B chromosome derived from the A complement.

Cytogenetic characterization of distinct B chromosomes in a population of the fish Astyanax bockmanni (Teleostei, Characiformes)

“…B chromosomes in several species of plants (Camacho 2005) and animals, including fish species (Poletto et al 2010), carry rRNA genes. However, in the present study, nucleolar activity or rRNA genes were not found in the B chromosome variants of A. bockmanni.…”

Discovering variation of secondary metabolite diversity and its relationship with disease resistance in Cornus florida L.

“…We first used discriminant analyses of principal components (DAPC) to identify collection sites that clustered together, according to SNP or metabolite abundance data. Using the R package adegenet (Jombart, 2008; Jombart, Devillard, & Balloux, 2010), we performed discriminant analysis (DA) on the optimal number of principal components (PC) to maximize among‐population variation and minimize within‐population variation. We estimated and analyzed PC scores separately from two different datasets (both scaled): reference SNPs aligning to the C. florida draft genome and abundance data (log‐transformed) for 377 metabolites.…”

Comparative cytogenetic mapping of rRNA genes among naked catfishes: implications for genomic evolution in the Bagridae family

“…By contrast, 5S rDNA signals were revealed in 2, 3, and 5 pairs of chromosomes in H. nemurus, H. wyckii, and H. filamentus, respectively. Multiple loci of minor ribosomal genes have been found in some fishes (Martins and Galetti, 2001;Hatanaka and Galetti, 2004;Rocco et al, 2005); variation in the number of 5S rDNA loci has also been observed among other species, such as the red wolf fish Erythrinus erythrinus, which has more than 20 sites (Cioffi et al, 2010), the cichlid Astatotilapia latifasciata, which has 15 clusters (Poleto et al, 2010) and the cichlid Laetacara dorsigera, which has 14 sites (Nakajima et al, 2012), In general, 5S rDNA loci can be found in the interstitial regions of fish chromosomes, and their pattern may represent an ancestral condition or even some advantage for the genome organization of these sequences (Martins and Galetti, 2001). H. wyckioides, M. atrifasciatus, and M. multiradiatus appear to maintain the ancestral location of the 5S rDNA loci, while the other genera studied had 5S rDNA loci at the terminal positions of the chromosomes.…”