Sex Chromosomes and Internal Telomeric Sequences in Dormitator latifrons (Richardson 1844) (Eleotridae: Eleotrinae): An Insight into their Origin in the Genus.

The freshwater fish species Dormitator latifrons, commonly named the Pacific fat sleeper, is an important food resource in CentralSouth America, yet almost no genetic information on it is available. A cytogenetic analysis of this species was undertaken by standard and molecular techniques (chromosomal mapping of 18S rDNA, 5S rDNA, and telomeric repeats), aiming to describe the karyotype features, verify the presence of sex chromosomes described in congeneric species, and make inferences on chromosome evolution in the genus. The karyotype (2n = 46) is mainly composed of metacentric and submetacentic chromosomes, with nucleolar organizer regions (NORs) localized on the short arms of submetacentric pair 10. The presence of XX/XY sex chromosomes was observed, with the X chromosome carrying the 5S rDNA sequences. These heterochromosomes likely appeared before 1 million years ago, since they are shared with another derived Dormitator species (Dormitator maculatus) distributed in the Western Atlantic. Telomeric repeats hybridize to the terminal portions of almost all chromosomes; additional interstitial sites are present in the centromeric region, suggesting pericentromeric inversions as the main rearrangement mechanisms that has driven karyotypic evolution in the genus. The data provided here contribute to improving the cytogenetics knowledge of D. latifrons, offering basic information that could be useful in aquaculture farming of this neotropical fish.

An Unusual Accumulation of Ribosomal Multigene Families and Microsatellite DNAs in the XX/XY Sex Chromosome System in the Trans-Andean Catfish Pimelodella cf. chagresi (Siluriformes:Heptapteridae).

This work constitutes the first cytogenetic characterization of a trans-Andean species of Heptapteridae. The catfish Pimelodella cf. chagresi from the Upper Rio Magdalena was studied, applying standard cytogenetic techniques (Giemsa, C-banding, and argyrophilic nucleolar organizer region [Ag-NOR]) and fluorescence in situ hybridization techniques using repetitive DNA probes: microsatellites (CA15 and GA15) and ribosomal RNA (rRNA) multigene families (18S and 5S recombinant DNA [rDNA] probes). The species showed a unique diploid chromosome number 2n = 50 (32m [metacentrics] +14sm [submetacentrics] +4st [subtelocentrics]) and a XX/XY sex chromosomal system, where the heteromorphic Y-chromosome revealed a conspicuous accumulation of all the assayed domains of repetitive DNA. P. cf. chagresi karyotype shares common features with other Heptapteridae, such as the predominance of metacentric and submetacentric chromosomes, and one pair of subtelomeric nucleolar organizer regions (NORs). These results reflect an independent karyological identity of a trans-Andean species and the relevance of repetitive DNA sequences in the process of sex chromosome differentiation in fish; it is the first case of syntenic accumulation of rRNA multigene families (18S and 5S rDNA) and microsatellite sequences (CA15 and GA15) in a differentiated sex chromosome in Neotropical fish.

A unique sex chromosome system in the knifefish Gymnotus bahianus with inferences about chromosomal evolution of Gymnotidae.

Cytogenetic studies in Neotropical electric knifefish of genus Gymnotus have shown a remarkable interspecific variability, including distinct sex chromosome systems. In this study, we present the first chromosomal data in Gymnotus bahianus from Contas River basin, northeastern South America. Based on extensive analyses, the modal diploid values were 2n = 36 (30m/sm + 6st) for females and 2n = 37 (32m/sm + 5st) for males. Therefore, a novel XX/XY1Y2 sex chromosome system is described for the genus. Single nucleolar organizer regions (NORs) interspersed to GC-rich sites were detected on a subtelocentric pair (7th) for both sexes and confirmed by fluorescent in situ hybridization with 18S rDNA probes. Heterochromatin was detected at pericentromeric regions of all chromosomes and interspersed to NORs on pair 7 and 5S rDNA cistrons on pair 9. The highly differentiated karyotype of Gymnoytus bahianus, with low diploid numbers and a unique XX/XY1Y2 system, reinforces the independent origin of sex chromosomes in Gymnotiformes and seems to reflect the particular evolutionary history of this species in a small and isolated drainage system. Moreover, in spite of morphological similarities, the present results indicate a remarkable chromosomal divergence in relation to closely related species such as G. sylvius and G. carapo.

Occurrence of freemartinism in Santa Ines sheep / Ocorrência de freemartinismo em ovino Santa Inês

This study reports a case of freemartinism of the XX/XY chimera type in a Santa Ines sheep belonging to a property in northeastern Para, Brazil. Discrete masculinization and external genitalia presenting a pseudoprepuce with a hypoplastic penis were observed in vivo. Anatomopathological examination of the internal genitalia showed the absence of a cervix and bilateral presence of an ovary and testis. Variable degrees of epididymal development, accompanied by agenesis of the deferent ducts and other structures arising from the mesonephric ducts, were also observed. Follicular structures, a uterine tubular portion, with marked agenesis and aplasia of the uterine tubes and in some portions of the horns, as well as other parts of paramesonephric structures, were noted in the ovaries. Blood was collected for karyotype analysis and 10 metaphases obtained by short-term lymphocyte culture were examined. Two cell lines were identified: 54,XX (5 cells) and 54,XY (5 cells).

Relata-se um caso de freemartinismo do tipo quimera XX/XY em ovino da raça Santa Inês, proveniente de uma propriedade no Nordeste Paraense (Brasil). In vivo observou-se masculinização discreta, genitália externa apresentando um pseudo-prepúcio com pênis hipoplásico. No exame anatomopatológico verificou-se na genitália interna a ausência de cérvix, ocorrência bilateral de ovário e testículo. Também se observou graus variáveis de desenvolvimento do epidídimo, com considerável agenesia dos ductos deferentes e outras estruturas provenientes dos ductos mesonéfricos. Nos ovários visibilizou-se estruturas foliculares, porção tubular uterina, com maior agenesia e aplasia das tubas uterinas e em algumas porções dos cornos, igualmente como outras partes das estruturas paramesonéfricas. A partir do sangue foi realizado a analise do cariótipo pela analise de dez metáfases, obtidas por cultura temporária de linfócitos, verificando a presença de duas linhagem celulares, sendo 54,XX (5 células) e outra 54,XY (5 células).

Ocorrência de freemartinismo em ovino Santa Inês / Occurrence of freemartinism in Santa Ines sheep

This study reports a case of freemartinism of the XX/XY chimera type in a Santa Ines sheep belonging to a property in northeastern Para, Brazil. Discrete masculinization and external genitalia presenting a pseudoprepuce with a hypoplastic penis were observed in vivo. Anatomopathological examination of the internal genitalia showed the absence of a cervix and bilateral presence of an ovary and testis. Variable degrees of epididymal development, accompanied by agenesis of the deferent ducts and other structures arising from the mesonephric ducts, were also observed. Follicular structures, a uterine tubular portion, with marked agenesis and aplasia of the uterine tubes and in some portions of the horns, as well as other parts of paramesonephric structures, were noted in the ovaries. Blood was collected for karyotype analysis and 10 metaphases obtained by short-term lymphocyte culture were examined. Two cell lines were identified: 54,XX (5 cells) and 54,XY (5 cells).(AU)

Relata-se um caso de freemartinismo do tipo quimera XX/XY em ovino da raça Santa Inês, proveniente de uma propriedade no Nordeste Paraense (Brasil). In vivo observou-se masculinização discreta, genitália externa apresentando um pseudo-prepúcio com pênis hipoplásico. No exame anatomopatológico verificou-se na genitália interna a ausência de cérvix, ocorrência bilateral de ovário e testículo. Também se observou graus variáveis de desenvolvimento do epidídimo, com considerável agenesia dos ductos deferentes e outras estruturas provenientes dos ductos mesonéfricos. Nos ovários visibilizou-se estruturas foliculares, porção tubular uterina, com maior agenesia e aplasia das tubas uterinas e em algumas porções dos cornos, igualmente como outras partes das estruturas paramesonéfricas. A partir do sangue foi realizado a analise do cariótipo pela analise de dez metáfases, obtidas por cultura temporária de linfócitos, verificando a presença de duas linhagem celulares, sendo 54,XX (5 células) e outra 54,XY (5 células).(AU)