RESUMO
The chromosomes of 2 flea beetle species from central Amazonia, Omophoita abbreviata and O. aequinoctialis (Alticini), were investigated through analysis of meiotic and mitotic cells. These species belong to the subtribe Oedionychina, a taxon that has unique cytogenetic features, such as giant sex chromosomes which are aligned at a distance during meiosis I (asynaptic). O. abbreviata and O. aequinoctialis have a meiotic formula of 10II + X + y, which is predominant in this subtribe. While the species of the genus Omophoita possess a relatively stable karyotype, a typical feature for Oedionychina, the present study identified inter- and intrapopulational variation in chromosome morphology, constitutive heterochromatin, and the presence and number of B chromosomes in O. aequinoctialis. In addition, FISH mapping of telomeric sequences revealed signals in the collochores, raising several questions on the chromosomal evolution in this group.
RESUMO
The genus Colomesus is the sole representative of the family Tetraodontidae in the Amazon region. Here, Colomesus asellus was analyzed using conventional and molecular cytogenetic protocols. Its diploid chromosome number is 2n = 46 with 12 meta-, 10 submeta-, 16 subtelo-, and 8 acrocentric chromosomes and a fundamental number of FN = 84. An XX/XY sex chromosome system was identified. Mapping of 18S rDNA correlated with the nucleolus organizer regions (Ag-NORs) in the short arms of the 2 X chromosomes in females and in the Y chromosome in males. C-banding revealed heterochromatin in the centromeric regions of all chromosomes, except for pair 3. Prominent sex chromosome-specific heterochromatin amplification was observed, covering the short arms of the Y chromosome almost entirely. FISH with telomeric and tropomyosin (tpm1) sequences, respectively, revealed terminal signals in all chromosomes. The analysis of extended DNA fibers confirmed the colocalization and the interspersed pattern of the telomeric and tpm1 sequences. Thus, this study highlights the remarkable evolutionary dynamism presented by the Amazonian puffer fish regarding the differentiation of a heteromorphic XY sex chromosome system and a particular sex-specific amplification of rDNA sites. This is the first record of such an association in the Tetraodontidae family.
Assuntos
Cromossomos Sexuais/genética , Processos de Determinação Sexual , Tetraodontiformes/genética , Animais , Antígenos Nucleares/genética , Brasil , Bandeamento Cromossômico , DNA Ribossômico/genética , Feminino , Amplificação de Genes , Hibridização in Situ Fluorescente , Masculino , RNA Ribossômico 18S/genética , Sequências Repetitivas de Ácido Nucleico , Telômero/genética , Telômero/ultraestrutura , Tropomiosina/genéticaRESUMO
Repetitive DNA is the largest fraction of the eukaryote genome and comprises tandem and dispersed sequences. It presents variations in relation to its composition, number of copies, distribution, dynamics, and genome organization, and participates in the evolutionary diversification of different vertebrate species. Repetitive sequences are usually located in the heterochromatin of centromeric and telomeric regions of chromosomes, contributing to chromosomal structures. Therefore, the aim of this study was to physically map repetitive DNA sequences (5S rDNA, telomeric sequences, tropomyosin gene 1, and retroelements Rex1 and SINE) of mitotic chromosomes of Amazonian species of teiids (Ameiva ameiva, Cnemidophorus sp. 1, Kentropyx calcarata, Kentropyx pelviceps, and Tupinambis teguixin) to understand their genome organization and karyotype evolution. The mapping of repetitive sequences revealed a distinct pattern in Cnemidophorus sp. 1, whereas the other species showed all sequences interspersed in the heterochromatic region. Physical mapping of the tropomyosin 1 gene was performed for the first time in lizards and showed that in addition to being functional, this gene has a structural function similar to the mapped repetitive elements as it is located preferentially in centromeric regions and termini of chromosomes.