We record the occurrence of male recombination, detected in cytological preparations of testes in 2 Drosophila willistoni population samples. Comparative analysis of meiotic figures in imaginal discs of testes and the salivary gland polytene chromosomes of male third instar larvae were employed. We observed anaphase bridges, suggesting the occurrence of chiasmata and fragmented chromatids involving the second chromosomal pair and the heterozygous inversions IILF and IILD+E segregating in the same individuals. This was observed in non-stressed larvae maintained at physiological temperature, and opens a wide field to study the factors that regulate crossing-over in natural populations of the highly polymorphic D. willistoni. We also observed what appears to be crossing-over in the tip of chromosomal arm IIL, in a sole male heterozygote for the inversion IILH of the G3 natural population.
The wild diploid species Gossypium capitis-viridis Mauer (2n=2x=26 B4B4) of Cape Verde Islands possess good fibre quality in addition to resistance to pest and diseases. Its narrow bracts ensure clean picking in cultivated cotton. An attempt was made to cross Gossypium arboreum var. MPKV GMS with Gossypium capitis viridis and doubled its chromosomes. The Chromosomes constitution of parents, F1, F2 and amphidiploid was confirmed. The hybridity of cross was confirmed on the basis of cytomorphological studies, pollen test and RAPD analysis. Cytological studies revealed that interspecific hybrid showed anomalous behavior of univalent and the formation of a single and double chromatin bridges at metaphase II that led to abnormal microspore formation in F1 and reduction in fertility. On an average chromosome association at metaphase were 0.976I+10.138II+0.06III+1.142IV and 0.84I+10.549II+0.053III+0.976IV in F1 and F2 of G. arbore-um×G. capitis-viridis, respectively. However, in amphidiploid generation mean chromosome conjugation formed were 0.832I+21.253II+0.05III+2.128IV. Random Amplified Polymorphic DNA (RAPD) analysis was employed to characterize the F1 interspecific hybrid of G. arboreum GMS×G. capitis-viridis, the doubled offspring and six segregants (designated 1–6). The 19 primers, selected from 43 initially screened, generated 250 amplification products of which 232 (92.8%) amplicons were polymorphic. Statistical analysis was carried out using NTSYS-pc software and a dendogram was generated using Jaccard's similarity coefficients. The values for similarity ranged from 0.31 to 0.66. Cluster analysis showed 3 main clusters. Cluster I consists of G. arboreum GMS, segregant 1, 2 and 4; cluster II comprises of G. arboreum GMS×G. capitis-viridis F1 and doubled offspring, segregant 5 and segregant 6 and cluster III consists of segregant 3 and G. capitis-viridis.
Eleven specimens of Iheringichthys labrosus, collected from the Tibagi River (Londrina, Paraná, Brazil) were analyzed cytogenetically, and were found to have a diploid chromosome number of 56, with a karyotype of 32M+8SM+6ST+10A and fundamental number (FN) of 102. In addition, supernumerary chromosomes or Bs varying from 0 to 3 were detected. C-banding revealed heterochromatin distributed mainly in telomeric regions, with a pair strongly stained on both telomeres. The B-chromosomes were totally heterochromatic. The restriction endonuclease (RE) AluI produced a band pattern almost similar to C-banding, and B-chromosomes showed no target sequences for RE.
Most of the widely grown banana cultivars are triploids (2n=3x=33). They are characterized by low male and female fertility and/or complete male and female sterility. On the contrary, diploids are generally both male and female fertile. Banana improvement programs use interploidy crosses to introgress useful genes from wild or improved diploids to triploid landraces. This study investigated the effects of meiotic irregularities on the fertility of diploid and triploid Musa accessions. Our results showed that precocious chromosomes movements, lagging chromosomes and univalents were observed in most of the accessions. In general, a higher incidence of univalent formation was related to low pollen fertility and polyspore formation.
Cytological studies of microsporogenesis in tetraploid (2n=4x=36) and apomictic accessions of Brachiaria nigropedata revealed chromosome transfer between microsporocytes in early meiosis. Six, in 20 accessions available at Embrapa Beef Cattle Research Center, presented cytomixis in frequencies ranging from 0.6 to 9.7%. The number of cells involved in the phenomenon varied from 2 to 4, with predominance of the first. Transference of a few chromosomes to the whole genome was found among cells. Prior to cytomixis, chromatin underwent structural alteration similar to what is observed in chromosome stickiness. This is the first report of cytomixis in the genus Brachiaria. Possible origin and implications to pollen fertility are discussed.
Several studies are being conducted to assess the toxicity and cytotoxicity of water bodies receiving industrial and domestic effluents, using the Allium cepa test. To assess the toxicity and mutagenicity of water possibly contaminated with chromium, derived from tannery activities, seasonal water samplings were performed in 2001 and 2002 at five different sites along the Sapucaizinho river, Municipality of Patrocínio Paulista, State of São Paulo, Brazil. A. cepa seeds were used as the test material and were submitted to germination in waters from the different collection sites, in Milli-Q water (negative control) and in aqueous solution of chromium (positive control). For the determination of cell division rates and mitotic irregularities, slides were prepared with root tip cells according to the standard Feulgen methodology. The results showed that the collection sites most heavily compromised by chromium emission presented low mitotic indices and a higher frequency of mitotic changes such as irregular anaphases (disorganized, multipolar, laggard), cells with chromosomal adherences, cells with micronuclei, and binucleate and/or multinucleate cells.
One male-sterile plant was recovered from a cross between pearl millet (Pennisetum glaucum) and its wild progenitor P. violaceum. The behavior of male sterility was temperature dependent, as the development of pollen mother cells to pollen grains was found to be dependent on temperature. The plant showed sterility at lower temperatures while it was fertile at higher temperatures during seasonal variations. This thermosensitive male sterility trait was found to be genetically controlled based on the segregation data of backcross generation. Segregation was observed for ca. 50% of the population expressing this trait. These TGMS plants exhibited transition from fertility to sterility when mean daily temperature reduced to ca. 20°C or below, and fertility was restored above this temperature. The period of 4 to 5 d prior to anthesis was found to be most sensitive to temperature variations. Chromosomal studies on the parent plant as well as segregants showed 2n=14 with regular meiosis during non-sensitive phase (period exhibiting male-fertility) ruling out aneuploidy and/or gross chromosomal structural aberrations as a cause of male sterility. Fertility characters were also studied for TGMS and non-TGMS plants during sensitive and non-sensitive phases. Pollen grains shed from the TGMS plants were much more vulnerable than from normal plants during sensitive phase indicating poor development of the membrane and walls of the pollen grains during sterility inducing conditions. Transition characteristics from male sterility to male fertility during sensitive and non-sensitive phases for TGMS and non-TGMS plants are discussed.
The cytogenetic analyses showed that Pseudopimelodus mangurus has a diploid number of 2n=54 chromosomes (6M, 26SM, 12ST and 10A), single Ag-NORs on the short arm of a middle-sized ST pair, identified as pair 19, and a very small amount of C-band positive segments in two chromosome pairs. The Ag-NORs are C-band positive. The staining of the chromosomes of P. mangurus with CMA3 reveled the occurrence of bright signals corresponding to the Ag-NORs segments, to the C-band positive segments and also to some C-band negative segments. The occurrence of a diploid number of 2n=54 in all species of the family Pseudopimelodidae and its absence among representatives of Pimelodidae and Heptapteridae, two related families previously considered, reinforces the hypothesis that Pseudopimelodidae is a monophyletic group.
Interspecific hybrid of Trifolium alexandrinum L. (Egyptian clover or berseem) with T. apertum Bobrov was developed through embryo rescue. Both the species are annual diploids (2n=16). Chromosomal pairing and fertility of F1 and F2 generation was studied with a view to understand the phylogenetic relationship of the two species and possibility of recombination between their respective genomes. The parental species showed regular bivalent formation followed by normal disjunction, pollen and seed fertility. Among six F1 hybrids, Hybrid 19, 20 and A-15-P1 showed multivalent formations at diakinesis while the rest three showed near normal bivalent formation. Pollen fertility among first generation hybrids was substantially high (>90%) except in Hybrid 19, which showed 78.7% pollen fertility. Variation for pollen size was also observed in Hybrids 19 and 20. 88.75 to 98.25% chromosomes contributed in bivalent formation. Among F2 plants, the meiotic behaviour was near normal and in most of the PMCs, eight bivalent formation was seen. F2 plants B-26-P1 and B-34-P1, however, showed formation of 0.2 quadrivalent and 0.33 trivalent per PMC respectively. Among other F2 plants infrequent formation of univalents was seen. In general, the plants showed more bivalents per PMC than that among F1 plants and 95 to 100% chromosomes associated as bivalents. Pollen fertility among these plants was also more than 95% in majority cases. Fertile F1 hybrids followed by fertile F2 generation and absence of segregation for fertility is an indicator that the two species are not differentiated by sizeable differences in their chromosomal/genic constitution and possesses close affinity.
The study deals with the effect of B-chromosomes on A-chromosome chiasma frequency, chiasma distribution and pollen fertility in Pennisetum typhoides. Results indicate that B-chromosomes enhance the number of interstitial chiasmata in A-chromosomes thereby increasing the chiasma frequency. Variation in chiasma frequency and distribution could be observed not only between carrier and non-carrier plants but also between carrier and non-carrier pollen mother cells (PMCs) of carrier plants. Mild reduction in fertility of carrier plants, in comparison to non-carriers, could also be noticed. The probable mechanism of B-chromosome action has been discussed in light of earlier works. Metaphase and anaphase behaviour of B-chromosomes have also been dealt with in brief.
Chromosome numbers, meiotic behavior, meiotic indexes and pollen fertility are presented for the first time for the native medicinal plant Maytenus ilicifolia (espinheira-santa). Intraspecific variability for chromosome number was verified among the 6 populations analyzed: 4 of them had n=32 chromosomes, one n=35 and the other n=40 chromosomes. Meiotic behavior was regular in the 4 populations studied. Meiotic index ranged from 95.8 to 100.0% and pollen fertility from 80.9 to 99.4%. M. ilicifolia chromosomes are very small (ca. 0.5 μm) and tend to clump therefore turning cytogenetic analysis, especially in somatic tissues a rather difficult task, what may partially explain the scarcity of cytogenetic studies so far performed in Maytenus and in the other genera of Celastraceae. Knowledge of the extension of intraspecific variability in chromosome number among M. ilicifolia populations is necessary for a better planned cultivation and breeding of this allogamous species in order to avoid decrease in fertility due to pollination between different cytotypes.
Several systems of sex chromosomes were described in fishes. Some of them are characterized by male heterogamety (XY/XX, X1X1X2X2/X1X2Y, XX/XY1Y2), others by female heterogamety (ZZ/ZW, ZZ/ZW1W2). In Tetraodontiformes, few multiple sex systems were reported. In the present work, specimens of Stephanolepis hispidus collected along the Bahia and Rio de Janeiro shore were cytogenetically analyzed. All individuals presented a diploid number of 2n=33/34 (NF=34), with 32 acrocentric chromosomes and a large submetacentric unpaired element in males and 34 acrocentric in females. An odder diploid number and the presence of 3 heteromorphic unpaired chromosome observed in the males, were characterized as a multiple sex chromosomal system of the type X1X1X2X2/X1X2Y. Ag-NOR marks were identified on a single chromosomal pair at interstitial position. Heterochromatic blocks were visualized at pericentromeric and centromeric regions. The presence of large chromosomes and a reduced diploid number indicates a chromosomal evolutionary pattern determined by centric fusions, similar to that observed in Balistidae species.
Water sources contamination is a major concern subject, as well as the environmental presence of a widely diffuse pollutants, as lead. Evaluation of xenobiont effects on genetic material have as a main objective to determine the relationships between genotoxicity and initiation of neoplasic and teratogenic events and genetic diseases. This evaluation can be done by means of several bioassays. Fishes are suitable bioindicators for the detection of aquatic pollution. In this study Oreochromis niloticus specimens were exposed to 2 different concentrations of (NO3)2Pb. Chromosome alterations in structure and number, micronucleus test and nuclear morphology alterations were analysed in chromosome preparations and blood smears of exposed and unexposed fishes. Results showed significant differences in the frequency of micronucleus and chromosome alterations between distinct treatments. These data suggest a genotoxic effect of (NO3)2Pb.
Chlorophyllin (CHL), a salt derivative of chlorophyll, has been demonstrated to be a potent agent against the deleterious action of different classes of mutagens. However, this effect depends largely on the test system, dose and conditions in which CHL is employed. The aim of this study was to examine in Allium cepa the toxic, cytotoxic and genotoxic effects of CHL and its capacity to inhibit such effects induced by the mutagenic agent mitomycin-C (MMC), under conditions of pre-treatment, post-treatment and concomitant treatment. The findings for this system indicate that CHL by itself does have toxic, cytotoxic or genotoxic effects. In examining the protective effect of this compound, CHL was not shown to reduce the cytotoxic effect previously produced by MMC in the first 20 h of treatment, but recovery from this effect was seen after 40 h. Under the conditions employed, this compound displayed an antigenotoxic or DNA-protective effect only immediately after treatment (20 h), being ineffective with the majority of concentrations tested after termination of the treatment.
In this study, the cytogenetic effects of a sulphonylurea group herbicide Logran (effective substance; Triasulfuron) were investigated in human peripheral blood lymphocyte culture. The cultures were treated with 2, 4, 8, 16, 32, 64, 128, and 256 μg/ml concentrations of Logran for 24 and 48 h. This compound increased chromosome aberrations (CA) in human lymphocyte culture. Logran decreased Mitotic Index (MI) related to the concentrations. Between the concentrations of 16 and 256 μg/ml Logran, this herbicide is cytotoxic and clastogenic in human peripheral blood lymphocyte culture treated in vitro.
Karyotypic studies on a population of Apareiodon affinis from Paraná river (Argentina) were carried out. Although the modal diploid number of the population was 54 chromosomes, some structural and numerical polymorphisms were detected. In the first case these variations deal with the number of mono- and biarmed chromosomes and in the second with the presence of an additional unpaired chromosome that appeared only in female individuals, suggesting some kind of linkage with a chromosomal system of sex determination. These data were compared with the available cytogenetic information and the geographic distribution of A. affinis.