摘要:

The term nucleosome has been reinvented by OUDET et al. (1975), ignoring or disregarding earlier proposals of the same term, to indicate the structural unit of the chromatin. Since this term means ‘nuclear body’, it is very inadequate to qualify a particular organization of the chromatin.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589193

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Chromosome behaviour in respect of chiasma distribution and frequency was studied in the pollen mother cells and embryosac mother cells of two populations each of wheat (Triticum aestivum) and oat (Avena sativa) and three populations of pearl millet (Pennisetum americanum). While regular bivalent formation was a normal feature in both the sex mother cells of oat with no variation observed in the chiasma frequency and distribution in male and female sex cells, in wheat one population showed regular bivalent formation in the two sex cells whereas the other population carried a reciprocal interchange involving two pairs of nonhomologous chromosomes in 80 and 71.42 per cent male and female sex cells, respectively. However, the presence of interchange did not effect the overall chiasma frequency which was almost similar in all the cells studied with or without a quadrivalent. In pearl millet, unlike oat and wheat, the chiasma frequency was higher in female sex cells than the male cells. Moreover, the distribution pattern of chiasmata varied drastically in the two sex cells at diakinesis and metaphase-I stages.It was predominantly terminal in male cells whereas in female cells interstitial chiasmata were mostly observed. It is concluded that in oat and wheat the contribution of the two sex cells towards generating variability through recombination are identical. In pearl millet it seems likely that the effective recombination is brought about chiefly by female meiotic bivalents and the male side provide for the retention of certain linkage groups. The importance of differential behaviour of chromosomes in the two sex cells is discussed.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589194

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Here, we report on the RAPD profiles of 61 individuals belonging to 10 macaque species. We used 23 different PCR primers on each sample and found an average of 17 bands per primer. The RAPD profiles appear to be highly reproducible because we found no differences in the amplification patterns produced by the DNA extracted from hair or blood. Strikingly, each species had a unique RAPD pattern homogeneously shared by all individuals. Comparisons between taxa showed that variability in the RAPD pattern was low, and the Sm index was below 0.601. Cluster analysis led to a division of the macaques into two main clusters: One withM. sylvanus and M. silenus and the other with M. arctoides, mulatta, fascicularis, nemestrina, tonkeana and fuscata. Macaca nigra and M. radiatawere positioned outside of these clusters. Gene flow may explain the zoogeographic pattern present in the RAPD profiles. The lack of within-species variability suggests the operation of founder effects and strong genetic drift, which may have been particularly strong in the case of peripherally placed species such asM. radiata, fuscata and nigra. The position of M. tonkeanais divergent from all the commonly accepted taxonomic and phylogenetic schemes. This result suggests that the RAPD technique is not always able to reveal the "true" phylogenetic relationships within the genusMacaca. The nature of genetic variation uncovered by the RAPD method is still unclear, and prudence should guide inferences about nucleotide divergence, population structure and phylogeny based solely on RAPD markers.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589195

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The Faba section of theViciagenus, which includes several widely distributed species in Mediterranean countries is considered the most evolved. Indeed, it is known nuclear DNA values range from 9.15 pg. (2C value) inVicia bithynica, to 26.56 pg. (2C value) in Vicia faba which has the highest DNA content in the genus. Banding pattern of metaphase chromosomes and nuclear DNA content in root meristematic cells of a Russian accession ofV. fabawere determined.Microdensitometric evaluation of nuclear absorption at different thresholds of optical density after Feulgen reaction indicated the organisation of the chromatin in-terphase nuclei. Karyotype, morphometric data and density distribution along the mid-rib of a chromatid were employed for the construction of a quantitative chromosome map generated by an automated image analysis system. The classification of Stebbins(1971), the TF%% values (Huziwara 1962) and Rec. and Syi indices (Greilhuber and Speta 1976) were used to perform the analysis. The results are compared with previous data concerningV. faba.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589196

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Seven species of the genusEucalyptuswere studied cytogenetically (E.deanei, E. dunni, E. grandis, E. maculata E. propinqua, E. saligna and E. tereticornis).The species showed a symmetrical karyotype with 2n=22 chromosomes,with chromosome length ranging from 0.58 m to 1.39 m. Karyotypic analysis indicated homogeneity of morphology and of chromosome number for most of the species of this genus studied here, although casual disploid species with 2n=24 have been found in previous studies. According to these data, a basic number of x=11 was established for this genus. The evolutionary tendency probably occurred by structural alterations (deletions, duplications, additions and translocations) and in some cases by aneuploid chromosome alterations.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589197

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Five cattle, two of the Podolian breed, two Grey Alpine, and one Chianina,all of which were heterozygous carriers of three centric fusion translocations(rob-l;29, rob-4;8, rob-25;27), underwent cytogenetic investigation. The use of G-, R- and C-banding patterns, combined with the FISH technique by using both type I molecular markers and some human chromosome painting probes, allowed the precise identification of chromosomes involved in the chromosomal abnormalities,compared to previous reports. While the chromosomes involved in the well known rob (1;29) were confirmed, BTA6 (not BTA4) was involved in the second translocation. Furthermore, BTA26 and BTA29 (not BTA25 and BTA27) were involved in the third translocation. C-banding patterns confirmed the mono-centric nature of rob (1;29) and revealed the dicentric nature of both rob(6;8) and rob(26;29). The importance of these marker chromosomes in bovid chromosome nomenclatures is also discussed.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589198

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The diploid number 2n=76 was found in five specimens (four males and one female) of a new species ofOryzomysbelonging to the nitidus group (Sigmodontinae,Rodentia) from Pacoti, state of Ceara, Northeastern Brazil. Cytogenetic data included CBG and GTG-banding, Ag-NOR staining as well as fluorescence in situ hybridization (FISH) with (T2AG3)n as probe, which revealed exclusive signals in all telomeres of all chromosomes. The karyotype comprises two large pairs(1 and 3) and four small metacentric pairs (34 to 37); 31 acrocentric pairs from large to small (pairs 2, and pairs 4 to 33). The X chromosome is a large subtelocentric and the Y is a medium size chromosome with two different morphologies:acrocentric and submetacentric. Pairs 1 and 3 are the result of Robertsonian rearrangements when compared with the 2n=80 karyotypes observed inOryzomys russatus, O. nitidus and O. emmomae. Interstitial telomeric sites (ITS) after FISH were not detected in those specific chromosomes.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589199

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Two groups of chlorophyll mutants of winter rye i.e. lethal and semilethal were compared in the present studies. Plants of the first group were characterized by pink orange or light violet colour of leaves at the seedlings stage. Plants with light green leaves, with yellow necrotic spots on leaves, or with white pattern and necrotic spots on leaves belonged to the second semilethal group. While plas-tids in pink and violet mutants were deprived of internal membrane organization in orange ones they had single thylakoids. In the second group of plants granal and intergranal thylakoids were present although the number of grana was reduced. The above changes in the plastid ultrastructure were accompanied by a lack of chlorophylls in pink, orange and light violet plants or strong reduction of both chlorophylls a and b in the remaining mutants. All the described features were inherited by single recessive genes.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589200

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The present work realized a comparative study in meiosis of two triatomines,Panstrongylus herreri and P. megistus, by cytogenetic techniques involving the restriction endonucleases Hae III andAluI and C-banding. The system of sex chromosomes inPanstrongylusis of the XXX2Y type, and experiments corroborated the common origin hypothesis of the X chromosomes by fragmentation of single X. In both species the restriction endonucleases (RE) presented banding patterns in part similar to C-banding. However, in some early meiotic phases it was possible to verify differentiation of the heterochromatic pattern. This work sug-' gests that other elements besides presence of recognition sites, such as chromatin packing degree and DNAprotein interaction, act in RE results, since digestion patterns occur in early spermatogenesis. However, metaphase chromosomes were practically inaccessible to the endonucleases.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589201

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Eleven species (including 18 samples) of the genusPyrenariacomplex, i.e.,Pyrenaria, TutcheriaandPampyrenariain the Camellioideae of the family Theaceae, were karyomorphologically investigated. Features common to all the species investigated include: (1) the simple chromocenter type of the interphasenuclei; (2) the chromosome number of 2n=30 and (3) the small chromosomes with the gradually decreased sizes. The basic chromosome number of x=15 is confirmed for all taxa. All species investigated are diploid. Only a few unimportant karyomorphological differences were found among these taxa, such as the variation of the number of the median, the submedian and the subterminal centromeric chromosomes, the mean arm ratio, the ratio of the longest chromosome length shortest chromosome length, and the karyotype asymmetry. These differences show no correlation with the morphological variation and the taxonomic circumscriptions of these taxa. Karyomorphological data provides further evidence for merging Tutcheria and Parapyrenaria into and establishing the genusPyrenariain its broad sense (Pyrenaria s.l.). Moreover, karyomorphological data suggest that Pyrenaria s.l. might have a close affinity with and is more primitive thanCamellia.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589202

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor