Cytogenetic characterization of F1, F2 and backcross hybrids of the Neotropical catfish species Pseudoplatystoma corruscans and Pseudoplatystoma reticulatum (Pimelodidae, Siluriformes)

The cytogenetic characteristics of Pseudoplatystoma corruscans and Pseudoplatystoma reticulatum and their F1, F2 and backcross hybrids were assessed by using chromosome banding techniques. The diploid number of 56 chromosomes was constant in all species and lineages, with a karyotypic formula containing 20 metacentric, 12 submetacentric, 12 subtelocentric and 12 acrocentric chromosomes. Nucleolar organizer regions (NORs) were identified in two subtelocentric chromosomes in the parents and hybrids, with partial nucleolar dominance in F1 and F2 specimens. Heterochromatic blocks were detected in the terminal and centromeric regions of some chromosomes in all individuals. For parental and hybrid lineages, 18S ribosomal clusters corresponding to NORs and 5S ribosomal genes were identified in distinct pairs of chromosomes. The striking conservation in the chromosomal macrostructure of the parental species may account for the fertility of their F1 hybrids. Similarly, the lack of marked alterations in the chromosomal structure of the F1 hybrids could account for the maintenance of these features in post-F1 lineages.

Intraspecific crosses resulting in the first occurrence of eight and nine B chromosomes in Prochilodus lineatus (Characiformes, Prochilodontidae)

B chromosomes are supernumerary elements present in about 15 percent of eukaryotic species and are most frequently heterochromatic, behave parasitically, show a transmission rate higher than standard (A) chromosomes, and can provoke harmful effects on carriers. In the current work, Prochilodus lineatus individuals carrying eight and nine B chromosomes were obtained by induced crossing performed involving breeders with different B chromosome numbers in their cells. The high B chromosome numbers found in the offspring were recorded for the first time in this species. The use of cytogenetic techniques applied in the present study revealed that regardless of the increase in number of B chromosomes in the genome of these individuals, those elements did not presented active genes, and showed their normal heterochromatic characteristic.

Cytogenetic markers as diagnoses in the identification of the hybrid between Piauçu (Leporinus macrocephalus) and Piapara (Leporinus elongatus)

The genetic monitoring of interspecific hybrids involves the application of methodologies able to provide an easy and indubitable genetic characterization of both parental and hybrid individuals. In the present work, cytogenetic techniques were used to identify a hybrid lineage of "Piaupara" in order to caracterize them in relation to the parental species, Leporinus macrocephalus (piauçu) and L. elongatus (piapara). The cytogenetic analysis revealed that L. macrocephalus presented 2n = 54 chromosomes and a nucleolar organizer regions (NOR) at the telomere of the long arm of the submetacentric chromosome pair 2. Analysis of constitutive heterochromatin (C-banding) revealed a conspicuous block at the pericentromeric region on the long arm of a submetacentric chromosome pair. L. elongatus presented the same diploid number, 2n = 54, and a karyotypic formula similar to that of L. macrocephalus. The NORs were also at the telomere of the long arm of the submetacentric pair 2, which was morphologically different from that of L. macrocephalus. Heterochromatic blocks were observed at both telomeres of a submetacentric chromosome pair. The hybrid "Piaupara" presented the same diploid number (2n = 54) and karyotypic formula as the parental species and there were no visible differences between parental and hybrid individuals. Differently from the Giemsa staining, NOR- and C-banding analysis showed marked differences which allowed the identification of the hybrids by the different morphology and/or size of the chromosomes carrying the NORs and patterns of heterochromatin distribution in their chromosomes. Such genetic studies are important for fish culture since they can provide tools for monitoring natural and artificial hybridization. They are also useful in biological conservation programmes and in the proper management of natural and reared fish stocks.

First report of a B chromosome in a natural population of Astyanax altiparanae (Characiformes, Characidae)

Several species of the genus Astyanax have already been genetically studied, and B-chromosomes have been considered to be an interesting feature in some species of this group. In the present paper we report, for the first time, the occurrence of a B microchromosome in a natural population of A. altiparanae. This additional genomic element was identified as an acrocentric chromosome, similar in size to the smallest chromosomal pairs of the standard karyotype. Analysis of the constitutive heterochromatin pattern by C-banding evidenced heterochromatic blocks located on centromeric, pericentromeric, and interstitial regions of some chromosomes, and also positive marks in a subtelocentric chromosomal pair that presented the short arms entirely heterochromatic. The application of this methodology also revealed a heterochromatic pattern in the extra chromosome, a typical feature of supernumerary chromosomes.

Estudo eletroforético da hemoglobina do cäo (Canis familiaris) / Electrophoretic study of canine hemoglobin (Canis familiaris)

Amostras de sangue de noventa cäes sem raça definida (SRD) de diversas idades e de ambos os sexos foram coletadas com EDTA, como anticoagulante e separadas as hemoglobinas com as técnicas usuais de laboratório. O fenótipo de cada animal foi obtido através de eletroforese em gel agar-amido, num sistema de tampäo descontínuo de pH 8,6, segundo a técnica de Matsubara com algumas modificaçöes. Foram identificados fenotipicamente duas bandas de hemoglobina, sendo a "A" mais forte e de migraçäo eletroforética lenta e a "B", mais fraca e de migraçäo mais rápida. Um dos animais apresentou, uma terceira, a "C", mais fraca e de migraçäo mais lenta que as anteriores. Näo foram observadas diferenças entre as hemoglobinas de cäes machos e fêmeas e entre adultos e jovens. Como os padröes encontrados contrastam com a literatura, onde a maioria das raças estudadas apresenta uma única banda, algumas hipóteses foram elaboradas para tentar explicar este polimorfismo

Complexo HLA e glaucoma crônico simples / HLA complex and chronic simplex glaucoma

Antígenos HLA-A e B foram determinados em 23 pacientes caucasóides portadores de glaucoma crônico simples. As freqüências antigênicas observadas foram comparadas às obtidas em amostras de populaçäo caucasóide de Säo Paulo. Os resultados obtidos näo revelaram associaçäo com nenhum antígeno HLA-A ou B isoladamente, porém sugeriram associaçäo com os haplotipos HLA-A9B12, A2B40 e A1B8. Estudo de distribuiçäo de haplotipos HLA entre irmäos portadores de glaucoma crônica simples ou de somente pressäo intraocular elevada revelou excesso de haplotipos em comum, sugerindo a presença no complexo HLA, ou próximo ao mesmo, de genes de susceptibilidade a glaucoma crônico simples

Efeitos do herbicida Roundup sobre a viabilidade ovo-adulto de Drosophila melanogaster / Effects of the Roundup herbicide on the egg-adult viability of the Drosophila melanogaster

No presente trabalho, foram estudados os efeitos do herbicida "Roundup" sobre a viabilidade ovo-adulto de quatro linhagens de Drosophila melanogaster: selvagem, "yellow", taxi e vestigial. A viabilidade foi medida através da contagem do número de indivíduos adultos nascidos a partir de um número conhecido de ovos, coletados em três tipos diferentes de concentraçäo de herbicida. Os resultados mostraram que houve uma reduçäo significante da viabilidade ovo-adulto, diretamente proporcional a concentraçäo do herbicida, isto é, quanto maior a concentraçäo, maior a reduçäo da viabilidade. Verificou-se, ainda, que as linhagens "yellow" e selvagem foram as mais resistentes aos efeitos do herbicida, enquanto que a linhagem vestigial foi a mais sensível

Bases genéticas da AIDS / Genetic basis of AIDS

A AIDS é uma doença moderna, altamente preocupante devido ao crescente número de pessoas contagiadas e a inexistência de medicaçäo ou vacina contra a sua açäo. O presente trabalho apresenta, em resumo, os aspectos genéticos da doença, sua origem, sintomatologia, diagnóstico e tratamento