Cytogenetic divergence between two sympatric species of Characidium (Teleostei, Characiformes, Crenuchidae) from the Machado River, Minas Gerais, Brazil

Cytogenetic studies were performed on two sympatric species of Characidium, C. gomesi and C. cf. zebra, from the Grande River basin, Minas Gerais State, Brazil. Although both species had a chromosome number of 50 with a karyotype exclusively consisting of meta- and submetacentric chromosomes, interspecific diversity was detected concerning the size of the two first chromosome pairs of the karyotypes. Active nucleolus organizer regions (NORs) were located at the terminal position on the long arm of the 17th pair of C. gomesi and at subterminal position on the long arm of the 23rd pair of C. cf. zebra. For both species the fluorochrome CMA3 stained only the NOR-bearing pair of chromosomes. The heterochromatin pattern also showed some differentiation between these species restricted to the centromeric or pericentromeric region of C. cf. zebra and practically absent in C. gomesi. These data are discussed concerning chromosome diversification in this fish group.

Cytogenetic analysis of three sea catfish species (Teleostei, Siluriformes, Ariidae) with the first report of Ag-NOR in this fish family

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Comparative cytogenetic and allozyme analysis of Mugil rubrioculus and M. curema (Teleostei : Mugilidae) from Venezuela

A comparative cytogenetic and allozyme analysis of sympatric specimens of Mugil rubrioculus and M. curema from Venezuela is reported. Specimens of M. rubrioculus exhibit a 2n=48 karyotype with exclusively acrocentric (NF=48) chromosomes, one pair of NORs interstitially located on chromosome pair number 8 and constitutive heterochromatin distributed in pericentromeric position of all chromosomes. Specimens of M. curema show cytogenetic features significantly different in comparison to M. rubrioculus in terms of chromosome number and morphology (2n=24 biarmed chromosomes, NF=48) and NORs location (telomeric region of the largest metacentric pair). Starch gel electrophoresis analysis at 20 presumptive loci reveals a reduced genetic difterentiation between the two species. In fact, though a total of ten private alleles are identified; all loci share alleles between the two species and the obtained Nei's genetic distance (D= 0.060) is lower than the values obtained between other congeneric mullet species. Thus, the cytogenetic and allozyme data sets indicate quite different degrees of genetic divergence between M. rubrioculus and M. curema. This could either reflect an underestimate of molecular divergence owing to cryptic variation or different rates of molecular/chromosomal evolution. Whatever the explanation, this study confirms the power of karyological data in discriminating species of Mugilidae.

CYTOGENETIC SURVEY OF SOME BRAZILIAN CERAMBYCIDAE (COLEOPTERA, POLYPHAGA, CHRYSOMELIDAE)

Meioformula was determined in 16 species of the family Cerambycidae, seven of them of the subfamily Cerambycinae, eight of Lamiinae and one of Prioninae. Only two species of Cerambycinae and one of Lamiinae showed the basic Polypliaga karyotype (9 + Xy(p)) and the remaining ones showed occurrence of centric fusions and fissions that have modified the basic karyotypes. These results are in accordance with previous studies on other species of this family.

The first cytogenetic report of fireflies (Coleoptera, Lampyridae) from Brazilian fauna

The first cytogenetic analysis of fireflies from Brazilian fauna was carried out in this work. The investigation of two species of the subfamily Lampyrinae, Aspisoma maculatum and Photinus sp. (aff. pyralis), showed the diploid number 2n = 19 and an X0 sex determination system in males. These observations are similar to those already described for all the Lampyrinae species previously studied. In contrast, Bicellonycha lividipennis (Photurinae) revealed the karyotype 2n = 16 + neoXY, which has not yet been registered for any firefly species. The neoXY sex determination system encountered in this species probably arose through fusion between an ancestral X sex chromosome, belonging to the X0 system, and an autosomal element. This event also reduced the diploid number from 2n = 19, which is more frequent in the family Lampyridae, to 2n = 18 in B. lividipennis. The analysis of meiotic cells showed that the neoXY sexual bivalent of B. lividipennis exhibited a prominent terminal chiasma, indicating that the sex chromosomes are not wholly differentiated and still retain a region of homology. A review of the cytogenetic data known for the family Lampyridae was also documented in this work, as well as a discussion on the main trends of chromosomal evolution that seem to have occurred in this group.

CYTOGENETIC EVIDENCE OF INVOLVEMENT OF CHROMOSOME REGION-15Q12 AND REGION-12Q15 IN CONDITIONS WITH ASSOCIATED OVERGROWTH

Syndromes with associated overgrowth are poorly understood. Besides their mode of inheritance, nothing is known regarding the basic genetic alterations that lead to their abnormal phenotypic manifestations. The chromosome localization of the genes involved remains unknown for this group of syndromes, with the only exception being the Wiedemann-Beckwith syndrome.

A SIMPLE TECHNIQUE FOR ISOLATION OF DNA SUITABLE FOR PCR AMPLIFICATION FROM CYTOGENETIC PREPARATIONS

In order to rescue molecular information from chromosome preparations, we describe a rapid procedure to obtain DNA from cytogenetic preparations in microscope slides, stored for one to live years at room temperature. This technique was modified from previously described procedures and the DNA obtained was shown to be suitable for PCR amplification.

Comparative cytogenetic studies of eleven species of the Tropidurus torquatus group (Sauria, Tropiduridae), with banding patterns

The chromosomes of 173 specimens representing eleven species of the Tropidurus torquatus group, from 33 localities in Brazil, were analysed after Giemsa staining, C-banding, NORs, and replication banding techniques. A karyotype with 2n = 36, including 12 macrochromosomes and 24 microchromosomes (12 M + 24 m), and sex determination of the XY:XX type were found in Tropidurus cocorobensis, T. erythrocephalus, T. etheridgei, T. hispidus, T. hygomi, T. montanus, T. mucujensis, T. oreadicus, and T. torquatus. The two other species, T. itambere and T. psammonastes, presented 2n = 36 (12 M + 23 m) karyotype only in females while males had 2n = 35 (12 M + 23 m), due to the sex determination of the X(1)X(2)Y:X(1)X(1)X(2)X(2) type. Other interspecific differences as well as some intraspecific variation regarding the NORs and C-banding patterns have been observed, mainly in the microchromosome set. on the contrary, the macrochromosomes were highly conservative. Although consistent karyotypic diversity occurred in the torquatus group, the cytogenetic data obtained up to now did not allow us to clarify the phylogenetic relationships of the species. Nevertheless, the geographical distribution of the distinct cytotypes in T. hispidus and T. torquatus suggested that more than one species might be involved in each case.

A SIMPLE AND FAST PROCEDURE TO GROW BAT FIBROBLASTS FROM LUNG BIOPSIES FOR CYTOGENETIC STUDIES

A fast, simple, and inexpensive procedure to establish fibroblast culture from bat lungs is presented. Explants plated following mechanical disaggregation provide good quality preparations for cytogenetics studies in about one week. Cultures established with this procedure may also be used for other biological studies.

CYTOGENETIC STUDIES ON THE SUBFAMILY HYPOPTOPOMATINAE (PISCES, SILURIFORMES, LORICARIIDAE) .3. ANALYSIS OF 7 SPECIES

Cytogenetic studies carried out on nine species belonging to five genera of the subfamily Hypoptopomatinae showed that this group has a relatively constant diploid number, 2n = 54, with only one species having 2n = 72 chromosomes. Nevertheless, the karyotypic formulae, NOR position and C-band pattern are very different among species and sometimes among local populations, with species having undifferentiated sex chromosomes and species having the XX/XY or the ZZ/ZW mechanisms. The population structure of species belonging to the subfamily Hypoptopomatinae suggests that many chromosome rearrangements have been fixed in the different species and populations due to their geographic isolation and these karyotypic differences may be very important today for species definition.