We analyzed cytogenetically specimens of Pimelodella meeki from Tibagi River at Limoeiro (LM) and from two tributaries, Couro do Boi (CB) and Gabriel da Cunha (GC) Rivers. All specimens presented 2n=46 chromosomes, which were the karyotypes composed by 15 pairs metacentric (M) + 6 pairs submetacentric (SM) + 2 pairs subtelocentric (ST). In specimens of GC, CB, and LM, the results of analyses of...

Nucleolar dominance describes the silencing of one parent's ribosomal RNA (rRNA) genes in a genetic hybrid. In Arabidopsis thaliana, rRNA genes are clustered in two nucleolus organizer regions, NOR2 and NOR4. In F(8) recombinant inbreds (RI) of the A. thaliana ecotypes Ler and Cvi, lines that display strong nucleolar dominance inherited a specific combination of NORs, Cvi NOR4 and Ler NOR2. The...

BACKGROUND Apart from a number of cases of inaccurate prognosis in regard to individual patients, the inter- and intra-observer variability of the classical, histological prognosis parameters have been under repeated discussion. For this reason, a long-term analysis was carried out in regard to overall survival by means of automated microscopic image analysis of the nucleolar organizer regions ...

The weakness of physical barriers in the marine environment and the dispersal potential of fish populations have been invoked as explanations of the apparent karyotype stasis of marine Percomorpha, but several taxa remain poorly studied cytogenetically. To increase the chromosomal data in this fish group, we analyzed cytogenetically three widespread Atlantic species from distinct families: Chae...

We have generated Dissociation (Ds) element insertions throughout the Arabidopsis genome as a means of random mutagenesis. Here, we present the molecular analysis of genomic sequences that flank the Ds insertions of 931 independent transposant lines. Flanking sequences from 511 lines proved to be identical or homologous to DNA or protein sequences in public databases, and disruptions within kno...

The 5S RNA genes of Drosophila melanogaster in either an isogenic wildtype or a multiply inverted (SM1) chromosome 2 increase their multiplicity when opposite a deficiency for the 5S gene site. This is analogous to the compensation phenomenon previously described for the 18S and 28S ribosomal RNA genes of the X chromosome nucleolus organizer region. Molecular hybridization of 5S RNA to DNA cont...

Concerted evolution is the production and maintenance of homogeneity within repeated families of DNA. Two mechanisms--unequal crossing over and biased gene conversion--have been the principal explanations of concerted evolution. Concerted evolution of ribosomal DNA (rDNA) arrays is thought to be largely the result of unequal crossing over. However, concerted evolution of rDNA in parthenogenetic...

Many students with learning disabilities (LD) experience difficulties with extracting relationships from expository text, especially if they are implicit. Results from studies with K-12 participants have been inconclusive regarding the potency of the graphic organizer (GO) as a comprehension tool. This study attempted to address some of the concerns with GO research by examining the effects of ...

Drosophila mulleri (MU) and D. arizonae (AR) are cryptic species of the mulleri complex, mulleri subgroup, repleta group. Earlier cytogenetic studies revealed that these species have different regulatory mechanisms of nucleolar organizing activity. In these species, nucleolar organizing regions are found in both the X chromosome and the microchromosome. In the salivary glands of hybrids between...

The chromosome modal number in Muscoidea Diptera is 2n=12, including five pairs of autosomes and one sex chromosome pair. Nevertheless, some species with 2n=10 chromosomes have been described, all of them from the Muscidae family. We analyzed the karyotype of some Muscidae species from different subfamilies and compared the obtained data with the karyotypes of some species of the families Calli...