摘要:

Successful crossing experiments between the tetraploidsAchillea ceretanica4x, A. collina, A. distanssubsp.styriaca, A. pratensis, and the octoploidA. monticola, all from theA. millefoliumagg. (Compositae), are reported. Chromosomes were studied in 514 out of 883 hybrid plants obtained from 13 crossings. Fi-offspring from tetraploid parents was generally tetraploid, but some combinations produced up to 30% of aneuploid, near-pentaploid, and even hexaploid F1-individuals. A backcross and a F2-progeny consisted of normal tetraploids. A reciprocal F1-combination involving a tetraploid parent with one B-chromosome showed an increase of B-chromosomes in the F1, when the male transmitted the B (69.2%), and a decrease, when the female had the B (33.3%). Mainly hexaploid offspring resulted from a reciprocal F1-cross between tetraploid and octoploid parents.

ISSN:0008-7114    

DOI:10.1080/00087114.1996.10797344

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

Chromosome analysis ofMuscina stabulanswith Giemsa and silver nitrate staining and C-banding revealed an example of an exception among Muscidae.M. stabulansalso presents the diploid chromosomal set consisting of 10 biarmed chromosomes, being 4 pairs metacentric and one pair submetacentric. None of the pairs was found heteromorphic. Positive but small C-band regions were always located on the centromeric regions of all chromosomes; an intersticial C + band appears only on the short arm of chromosome 2. In meiotic plates only chromosome 2 was observed bearing one Ag-NOR site on the short arm too.

ISSN:0008-7114    

DOI:10.1080/00087114.1996.10797345

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

Peripheral blood lymphocytes were cultured by conventional methods in order to harvest metaphase cells. Slides were air dried and incubated in phosphate buffer at high temperature in order to study chromosome ‘dots’. Our previous investigations had indicated that chromosomes of undifferentiated cells (lymphoblasts) contained numerous heterochromatic ‘dots’, while chromosomes of patients with acute lymphoblastic leukemia (ALL) contained an elevated dot frequency. In this investigation, however, chromosomes of differentiated lymphocytes were found to contain no distinct dots. This finding indicates that a reduction of heterochromatic dots in chromosomes is correlative to cellular differentiation.

ISSN:0008-7114    

DOI:10.1080/00087114.1996.10797346

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

Blood cells from 22 river buffaloes (Bubalus bubalisL., 2n = 50) raised in the South Italy were cultured for both early—and late—incorporation of BrdU so as to obtain G- and R-banding, respectively. Slides were sequentially treated for G-banding/Ag-NOR and R-banding/Ag-NOR techniques. These procedures allowed to identify which chromosomes carry the NORs and the frequency of active NORs per NO-chromosome. According to the standard nomenclature, NORs in river buffalo are located at the telomeres of chromosomes 3p, 4p, 6, 21, 23 and 24 while the frequencies of active NORs per NO-chromosome were higher in chromosomes 4p, 23 and 24 (64.8%, 70.2% and 72.2%, respectively) than in chromosomes 3p, 6 and 21 (42.1%, 17.3% and 28.1%, respectively).

ISSN:0008-7114    

DOI:10.1080/00087114.1996.10797347

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

Cytogenetic studies on Bryconid fishes have shown the occurrence of karyotype and NOR conservatism and heterochromatin reorganization. The present data on three species representative of the migratory genusBryconcorroborate the hypothesis according to which conservative patterns of karyotypic evolution can be related to high levels of vagility and large populational size in Neotropical freshwater fishes.

ISSN:0008-7114    

DOI:10.1080/00087114.1996.10797348

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

The localization of callose during meiotic and apomeiotic megasporogenesis in diploid species of the genusMedicagowas investigated by fluorescence microscopy. Callose deposition and cytoembryological details were studied by treating flowers with a clearing/staining medium. Ovules were classified into different developmental stages and the distance of growing integuments from the micropyle measured. The relationship between the stage of development and the growth of integuments proved to be an effective method for correlating megasporogenesis events with callose deposition and assessing the cytological mechanism of apomeiosis. Within meiotic ovules callose deposition appeared as thin micropylar caps in the megaspore mother cells and as thick cell plates between dyad, triad and tetrad cells. The degradation of callose started at the beginning of embryo sac differentiation. Ovules with diplosporic cells were characterized by complete absence of callose. When callose was present at the megaspore mother cell level, it seemed not to completely isolate the sporogenous cells from the surrounding somatic cells of the nucellus. Callose deposition between or around the micropylar megaspores may exert a negative selection towards them, and so determine the functionality of the only chalazal megaspore. According to this hypothesis, the absence of callose in diplosporic cells of the apomeiotic mutant may be the effect rather than the cause of diplospory.

ISSN:0008-7114    

DOI:10.1080/00087114.1996.10797349

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

The G-band karyotype ofAkodon lindberghi(2n= 42, FN = 42) has been described in eight wild caught specimens captured outside its type locality, C-banding showed distinct heterochromatic regions at the centromere of all chromosomes. Ag-NOR staining showed a maximum of 12 NORs per cell per individual with a mean number of 1.4 per metaphase.

ISSN:0008-7114    

DOI:10.1080/00087114.1996.10797350

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

The present cytogenetic study performed in argentine populations ofSynbranchus marmoratusshows clear differences between the brazilian samples analized by FORESTIet al.(1992). The results obtained indicate only one chromosomic number from all samples, 2n= 44 (4M-SM + 40 ST-A) and the existence of multiple C-bands either in pericentromeric or interstitial position. Also multiple NORs (on several different chromosome pairs). Were detected the existence of one specimen carrying a small accessory chromosome caracterized as one metacentric and heterochromatic element. Intraindividual polymorphism involving the lenght of pair three was found in all the specimens analized. The comparison between the present data and the available bibliography shows clearly the presence of more than one taxonomic entity withinSynbranchus marmoratus.

ISSN:0008-7114    

DOI:10.1080/00087114.1996.10797351

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

The karyotype of the four species belonging to different genera of the Sorubiminae subfamily was analysed. In spite of some differences in chromosomal structure, all species showed the same diploid number (2n= 56) and a single NOR system which was always present in submetacentric chromosomes. C-banding pattern has been extremely conserved in this group, with heterochromatic blocks preferentially in telomeric and pericentromeric regions. In this subfamily the great karyotypic homogeneity is contrasted with the great variability of the Pimelodidae family.

ISSN:0008-7114    

DOI:10.1080/00087114.1996.10797352

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor

摘要:

Some species ofHypostomusfrom the Upper Paraná Basin (SP) were studied cytogenetically. The diploid chromosome number ranged from 2n= 68 to 2n= 80, with a considerably variable karyotypic structure between species, but no chromosomal differences were observed between males and females. The nucleolar organizer regions (NORs) were also quite variable both intra- and interspecifically in terms of number and size. In general, constitutive heterochromatin was not very abundant and usually located in small blocks. The data suggest that some chromosomal rearrangements, as the robertsonian ones and pericentric inversions, were important for the karyotypic evolution ofHypostomus.These fishes also appear to be a good material for cytotaxonomic studies.

ISSN:0008-7114    

DOI:10.1080/00087114.1996.10797353

出版商:Taylor & Francis    

年代:1996

数据来源: Taylor