Chromosome studies in some Stevia. Cav. (Compositae) species from Southern Brazil

Karyotypes of six species of the genus Stevia from Southern Brazil were studied, utilizing root tip metaphases. All species were diploid with 2n = 22 chromosomes. It was possible to identify each species by chromosome morphology. The basic chromosome number for Brazilian species of Stevia is X = 11. This number is also found in almost all South American species. We suggest that in Stevia there is an evolutionary trend toward chromosomal rearrangement, caused mainly by pericentric inversions. It was found that, in addition to aneuploidy and polyploidy, chromosomal rearrangements are common in the tribe Eupatorieae.

Chromosome damage in underground coal miners: detection by conventional cytogenetic techniques and by submitting lymphocytes of unexposed individuals to plasma from at-risk groups

Chromosome abnormalities and the mitotic index in lymphocyte cultures and micronuclei in buccal mucosa cells were investigated in a sample of underground mineral coal miners from Southern Brazil. A decreased mitotic index, an excess of micronuclei and a higher frequency of chromosome abnormalities (fragments, polyploidy and overall chromosome alterations) were observed in the miners when compared to age-paired normal controls from the same area. An alternative assay for clastogenesis in occupational exposition was tested by submitting lymphocytes from non-exposed individuals to a pool of plasmas from the exposed population. This assay proved to be very convenient, as the lymphocytes obtained from the same individuals can be used as target as well as control cells. Also, it yielded a larger number of metaphases and of successful cultures than with common lymphocyte cultures from miners. A significantly higher frequency of chromatid gaps, fragments and overall alterations were observed when lymphocytes from control subjects were exposed to miner plasma pools. Control plasma pools did not significantly induce any type of chromosome alterations in the cultures of normal subjects, thus indicating that the results are not due to the effect of the addition of plasma pools per se.

TP53 mutations and loss of heterozygosity of chromosome 17 in colorectal tumors

The incidence of TP53 point mutations and loss of heterozygosity (LOH) of chromosome 17 in colorectal tumors was determined in a group of Brazilian patients. We screened DNA samples from tumors and distal normal mucosa of 39 patients with colorectal cancer, for TP53 mutations by PCR-SSCP (single-strand conformation polymorphism) analysis. Chromosome 17 LOH was investigated using six PCR-based polymorphic markers and one VNTR probe. TP53 mutations were demonstrated in 15/39 of the cases. Mutations were distributed among all exons examined (five to eight), the majority of them being G/C to A/T transitions. LOH of chromosome 17p and 17q was detected in 70 and 46% of the tumors, respectively. There was a significant association between TP53 mutations and LOH in chromosome 17p (P = 0.0035) and 17q (P = 0.03). Although no correlation was observed between TP53 genetic alterations and clinical/ pathological characteristics, the association of TP53 mutations with loss of both chromosome 17 arms may indicate that TP53 inactivation provokes an unstable phenotype in tumor cells in colorectal tumors.

Reading the human Y chromosome: the emerging DNA markers and human genetic history

Reading the human Y chromosome: the emerging DNA markers and human genetic history.

Chromosome polymorphism in Ctenomys minutus (Rodentia-Octodontidae)

A sample of 101 specimens of Ctenomys minutus was collected along its geographic range. Eight karyotypes (2n = 42, 45, 46a, 46b, 47, 48, 49 and 50) were found. The chromosome polymorphisms were due to Robertsonian rearrangements and tandem fusions. The distribution of polymorphisms indicated three population blocks: northern (2n = 49 and 50), central (2n = 46a, 47, and 48) and southern (2n = 42, 45, and 46b). These findings suggest that this species is undergoing a speciation process due to geographic isolation.

Recuperation and improvement of chromosome preparations stained with silver nitrate

Both periodic acid and photographic reagents have been used to remove the silver nitrate residues from cytological preparations. We used potassium ferricyanide to remove AgNO3 salts in cases of excessive chromosome impregnation. This method produced partial decolorization, with contrast enhancement. Counterstaining with Giemsa also promoted a better contrast between chromosome arms and NORs, which were preserved and retained a dark color. Application of this procedure to chromosome preparations treated sequentially for CBG banding/AgNO3 staining promoted complete decolorization of C+ regions, leading to "reverse" C-banding, generally with high contrast.

Chromosome number in germplasm accessions of Paspalum notatum (Gramineae)

Chromosome numbers are reported for 127 germplasm accessions of Paspalum notatum maintained by EMBRAPA (Empresa Brasileira de Pesquisa Agropecuária) in two research centers in Brazil. Most accessions were collected in their natural habitats in Southern Brazil. Tetraploidy (2n = 40 chromosomes) was predominant (91% of the accessions studied), confirming previous reports for the species. Eleven accessions with 2n = 20 chromosomes, although collected in the wild, are possibly derived from 'Pensacola' bahiagrass, commonly cultivated in the area since its introduction from the United States in the 60's, for the establishment of permanent pastures.

Chromosome sensitivity to bleomycin in G2 lymphocytes from Down syndrome patients

Several studies have demonstrated that lymphocytes from patients with Down syndrome (DS) exhibit an increased frequency of chromosome aberrations when they are exposed to ionizing radiation or to chemicals at the G0 or G1 phases of the cell cycle, but not at G2, when compared to normal subjects. To determine the susceptibility of DS lymphocytes at G2 phase, bleomycin, a radiomimetic agent, was used to induce DNA breaks in blood cultures from 24 Down syndrome patients. All the patients with DS showed free trisomy 21 (47,XX + 21 or 47,XY + 21). Individuals that showed an average number of chromatid breaks per cell higher than 0.8 were considered sensitive to the drug. No control child showed susceptibility to bleomycin, and among the 24 patients with DS, only one was sensitive to the drug. No significant difference was observed between the two groups, regarding chromatid break frequencies in treated G2 lymphocytes. The distribution of bleomycin-induced breaks in each group of chromosomes was similar for DS and controls. No significant difference was found in the response to bleomycin between male and female subjects. Probably, the main factor involved in chromosome sensitivity of lymphocytes from patients with DS is the phase of the cell cycle in which the cell is treated.

Family names and the length of the Y chromosome in Brazilian blacks

The variability of the lengths of the heterochromatic and euchromatic segments of the human Y chromosome was studied by a quantitative method of densitometric measurement in 60 normal and unrelated black individuals (30 with and 30 without devotional surnames), living in Salvador, Bahia, northeastern Brazil. Thirty normal and unrelated Caucasian individuals of European origin, living in Curitiba, Paraná, south Brazil, were included as controls. The heterochromatic segment and total Y chromosome lengths were greater in caucasians than in blacks without devotional surnames, and these were greater than in blacks with devotional surnames. These findings are in agreement with previous reports of a higher percentage of black ancestry in blacks carrying devotional surnames than those carrying non-devotional ones.

Effect of taxol on chromosome aberrations induced by gamma radiation or by doxorubicin in Chinese hamster ovary cells

Combined therapy with radiation and chemotherapy has being increasingly used in cancer treatment. The effect of combinations of taxol (0.08 mug/ml) with doxorubicin (DXR, 0.5 or 1.0 mug/ml) or gamma radiation (20 or 40 cGy) was examined in two different treatment schedules (pretreatment or simultaneous treatment) using Chinese hamster ovary (CHO) cells treated at the G2 phase of the cell cycle. The results showed that taxol did not have a radiosensitizing effect on the chromosomal aberrations induced by gamma radiation nor did it have a potentiating effect on the chromosomal aberrations induced by DXR in CHO cells treated in the G2 phase of the cell cycle

Chromosome studies in southern Brazilian wheat pest aphids Sitobion avenae, Schizaphis graminum, and Methopolophium dirhodum (Homoptera: Aphididae)

We examined the chromosome set of the aphid species Sitobion avenae, Schizaphis graminum and Methopolophium dirhodum by means of conventional staining and C, NOR, AluI and HaeIII banding methods. These species are considered important pests to several plants of economic interest in Brazil. No variation was observed in the number of chromosomes of S. avenae, whereas there was intraspecific variation in the other two species. Interspecific differences in the response to the banding treatments were observed. Whereas these techniques allowed the identification of several S. graminum chromosome pairs, only the AluI treatment was capable of inducing differential staining in the M. dirhodum chromosomes and no clear patterns emerged when the S. avenae preparations were treated

Chromosome number and secondary constriction variation in 51 accessions of a citrus germplasm bank

The mitotic chromosomes of 51 citrus accessions from the Centro Nacional de Pesquisa em Mandioca e Fruticultura Tropical, Cruz das Almas, BA, Brazil, were analyzed. The sample included representatives of 20 Citrus species, one of Poncirus and seven hybrids. All accessions showed 2n = 18 without any evidence of numerical variation. The most clearly variable karyotype feature was the number and position of secondary constrictions (SECs). In 19 accessions the SECs were not identified, mainly due to the degree of chromatin condensation. In the remainder they varied in number from one to three per karyotype. They were found in the proximal region of one of the three largest chromosome pairs, in the terminal/subterminal region of a smaller chromosome or, more seldom, terminally in a larger chromosome. Only in a few cases were such constrictions observed simultaneously in both homologues of the same chromosome pair. The high variability of this karyotype feature may be due to the activation of this region in the previous interphase but may also indicate a high structural variability and heterozygosity of citrus germplasms

Deletion/inversion in the X-chromosome and increased telomeric associations in a female with primary amenorrhea

We describe a new case of a partial interstitial deletion and inversion of the long arm of the X-chromosome associated with a high incidence of telomeric associations in an 18-year old female who showed underdeveloped secondary sex characteristics, including small breasts and primary amenorrhea. Her karyotype was considered to be 46,X,del(Xq13 -> q22)inv(X)(q23-q27). The buccal mucosal cells showed absence of a typical Barr body, and the 5’-bromo-2-deoxyuridine incorporation studies revealed that neither the normal X-nor the abnormal X-chromosome was late replicating. The case is being presented for its extreme rarity

Chromosome study in two Aratinga species (A. guarouba and A. acuticaudata) (Psittaciformes)

The karyotypes of two species of Psittacidae of the genus Aratinga, Aratinga guarouba and A. acuticaudata were studied for the first time. The metaphases were obtained using a short term culture of feather pulp. These karyotypes are compared with others of the genus and their karyological relationships in the Psittaciformes are discussed

Study of a region on yeast chromosome XIII that complements pet G199 mutants (COX7) and carries a new non-essential gene

The mutants of Saccharomyces cerevisiae assigned to complementation group G199 are deficient in mitochondrial respiration and lack a functional cytochrome oxidase complex. Recombinant plasmids capable of restoring respiration were cloned by transformation of mutants of this group with a yeast genomic library. Sequencing indicated that a 2.1-kb subclone encompasses the very end (last 11 amino acids) of the PET111 gene, the COX7 gene and a new gene (YMR255W) of unknown function that potentially codes for a polypeptide of 188 amino acids (about 21.5 kDa) without significant homology to any known protein. We have shown that the respiratory defect corresponding to group G199 is complemented by plasmids carrying only the COX7 gene. The gene YMR255W was inactivated by one-step gene replacement and the disrupted strain was viable and unaffected in its ability to grow in a variety of different test media such as minimal or complete media using eight distinct carbon sources at three pH values and temperatures. Inactivation of this gene also did not affect mating or sporulation