摘要:

A revision ofTulbaghia(Alliaceae) has been carried out. The genus includes twentyone species and one variety. On the basis of the different karyotypes, the genus can be subdivided into seven distinct Groups. Some species have poly-ploid forms but no true polyploid species has been found so far. A number of species possess heterochromatic segments which may be either mostly distally or proximally located. The heterochromatic segments ofTulbaghiaare cold sensitive and specific fluorochrome staining shows that they are composed mainly of highly repetitive sequences of Guanine-Cytidine nucleotides. The possible evolutionary role of heterochromatin as well as that of the B-chromosomes, present in some species, is briefly discussed. The illustrations include micrographs of the mitotic chromosomes as well as colour photographs of the inflorescence of all the species. The typical habitat of two of the species is also illustrated in colour.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589184

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Influence of varying temperatures i.e. 31°C, 44.4°C, and 36°C on the:behaviour of chromosomes was studied in the pollen mother cells (pmcs) and embryo-sac mother cells (ernes) ofCrotalaria junceaL. While meiosis in both the sex cells at 31°C was normal with perfect bivalent formation observed in cells at diplotene/diakinesis and metaphase-I stages, abnormal meiosis, characterized by the failure of synapsed chromosomes to retain chiasmata at diakinesis and later stages resulting in the formation of varying frequencies of univalents, was a common fea ture at 44.4°C. Interestingly, the felling apart of homologues was found to be spe- ; cific to microsporogenesis and megasporogenesis showed normal synapsis. However, with a subsequent fall in temperature to 36°C, all the pmcs restored their normal pairing behaviour. The possible causes of such differential behaviour of chromosomes in the two sex cells and its significance is discussed.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589185

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Somatic chromosomes were studied from roots from seven species and two varieties of the genusOpuntiacollected from different localities in Eastern India. 2n = 22 chromosomes were observed in four, 2n = 44 in two and 2n = 55 chromosomes in one population. The total chromosome length is maximum in O.Ficus-indica(2n = 55) and minimum in O.microdasysvar. lutea (2n = 22). The karyotypes show a similarity in basic number x = 11, except for the horticultural variety, O.monocantha variegatawith 2n = 34. The chromosome sizes range from very small (0.97 mm) to medium (3.46 mm); the primary constriction varies from nearly submedian to median and the numbers of chromosomes with secondary constrictions are from four to six. Numerical analysis of data indicates a general similarity of the karyotypes, with O.Ficus-indicaoccupying a separate position.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589186

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Reproduction of natural hybridH. x desetangsii nothosubsp.carinthiacum(H. perforatum L. x H. maculatum Crantz subsp. maculatum) of three different ploidy levels was studied. Facultative and pseudogamous apomixis is known in H.perforatumthat represents mother plant of the hybrid studied. Selfing, backcrossing of the hybrid as well as crossings with other taxa were carried out. Chromosome numbers of the offspring obtained after the performed pollinations were counted in order to explain its origin. Presented results confirmed the occurrence of facultative apomixis with pseudogamy in the hybrid studied. Various ploidy levels from triploid to heptaploid ones as well as aneuploids and mixoploids were found among the progeny.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589187

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Two flying squirrel species,Pteromys momongaandPteromys volanscontain 2nequals;38 with the same fundamental number of 68, but differ in their karyotypes. Almost all the autosomes and the sex chromosomes have either complete or partial G-band correspondence, and thus provide definitive evidence for the taxonomic relationship of thesePteromysspecies. The karyotypic differences occurred as results of pericentric inversion, tandem fusion, and deletion of autosomes and the Y chromosome. No Robertsonian event occurred. Both species possess one pair ofAg-NORs in identical G-banded chromosomes but different morphology resulting from pericentric inversion. Despite the conservatism of G-band patterns, a striking accumulation of C- heterochromatin has occurred in theP. momongakaryotype. Flow-cytometric DNA determination demonstrated that P.volansgenome contains approximately 15 %% less DNA. These differences seem to be prima rily reflected by chromosomal deletions in the P.volanskaryotype rather than ac cumulation of the Cheterochromatin in the P.momongakaryotype. The present findings are crucial for explaining the direction of karyotype evolution of these species, and suggest that the karyotype of P.momongais ancestral and that P.volansis derived from it.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589188

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A synaptonemal complex (SC) study of specimens of Nellore and Gyrbreeds of Bostaurus indicuswas performed with the main objective to identify and determinate the frequency of abnormalities of SC and the frequency of cells with abnormalities. All animals analyzed had 29 autosomal bivalents and one sexual bivalent. The Nellore breed had 30.00% of cells with SC abnormalities while the Gyr breed had only 11.11%. Statistical analyses showed that there were not significant differences for the number of cells with abnormalities among the breeds studied. The subspecies Bos taurus indicus had 16.92% of cells showing abnormalities, being 62.82% of these abnormalities in zygotene and 37.18% in pachytene. Some aspects regarding the frequency of cells with abnormalities and the fertility of Nellore and Gyr breeds are discussed.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589189

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The analysis of 9 populations ofEcheandia nanashowed all to be diploid,with2n= 16, n −. 8 (x = 8). The analyzed populations displayed two cytotypes.Cytotype A − 10m+6sm, having two pairs of chromosomes with a satellite, was observed in four populations from the eastern flanks of the Pachuca mountain range. The five remaining populations from the western flank of the Pachuca and Sierra Nevada mountain ranges (Mexico) showed cytotype B + 6m+8sm+2st, having one pair of chromosomes with a satellite. The analysis of meiosis revealed heterozygotic exchanges. Analysis of MI showed three heteromorphic bivalents in cytotypes A and B. Analysis of AI showed sub-chromatid aberrations, (side arm bridges = SAB), which were more frequent in cytotype B (39.88+44.84%) than in cytotype A (2.86+31+53%). Cells with two bridges (SAB aberrations) were observed in cytotype B.The intraspecific cytological and genical differentiation of cytotypes A and B is probably the result of geographical isolation between populations of E. nana. This suggests that this species is undergoing through a major process of genomic differentiation involving heterozygotic chromosomal rearrangements; which favors a process of speciation between both cytotypes without the occurrence of significant morphological changes. This cytological and genical differentiation between cytotypes A and B was evident in the significant differences of the low number of fruits and viable seeds produced after cross-pollination among cytotypes (AxB: 0–16 fruits; 0–448 abortive seeds), relative to the larger values recorded after crosspollination within cytotypes (AxA: 4–48; 152–1824) (BxB: 3–89; 14–3382).

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589190

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Meiotic studies of pollen mother cells and nuclear 4C DNA content inten species ofFerocactus(Cactaceae) revealed significant interspecific variations.The haploid chromosome numbern=11was found in all the studied species. The chiasma frequency per nucleus varied from 18.20 in F. echidne to 21.75 in F.gracilisin meiotic metaphase I. The formation of univalent's in some of the cells and/or spindle anomalies lead to the formation of pentads, hexads or octads. Pollen sterility varied between 7.66% in F. emoryi to 9.74% in F.gracilis. The 4C DNA content in root tip cells varied from 7.37 pg in F.histrixand 9.74 pg in F.gracilis. Significant variations of in situ nuclear DNA content as well as chiasma number per bivalent was evidient in interspecific level.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589191

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A variation in the karyotype ofAlouatta fusca clamitamfrom different geographical ranges is presented. Blood samples of six captive specimens from different States of Brazil were analyzed. Distinct diploid numbers were found: 2n=52, 2n=45 and 46. The odd number was due to Y-autosome translocation. The comparison of the G-banding patterns with previous published reports of 2n=49 and 50 allowed us to identify Robertsonian rearrangements and pericentric inversions as the most important chromosomal rearrangements involved in the differentiation of the observed cytotypes. The finding of specific cytotypes associated to different geographical ranges suggests a northern-southern division ofAlouatta fusca damitans,due to a possible reproductive isolation between different chromosomal complements.The fixation of such rearrangements could have occurred during the existence of the quaternary refuges, when the populations have been disrupted in smaller denies.

ISSN:0008-7114    

DOI:10.1080/00087114.2000.10589192

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor