摘要:

The structure and behavior of the kinetochore during meiotic divisions were observed in microsporocytes ofTrillium kamtschaticumusing the acetocarmine squash method. The kinetochore region assumes a drumstick shape throughout metaphase-I to metaphase-II, and it consists of (1) the spherule, which has been referred to as the kinetochore, and (2) the chromonematic fibers, which connect the kinetochore with both arms of the chromosome. At metaphase-I the kinetochore region is stretched out on both sides of the bivalent. At this stage two adjacent kinetochores can be seen in each homologue, evidently representing the two sister kinetochores organized by the underlying duplicated chromatids. The sister kinetochores remain closely associated throughout anaphase-I to telophase-I, lying on the same side of each homologue. At metaphase-II the kinetochore region is again stretched out from the chromosome (dyad), and at this time the sister kinetochores still lie on the same side of the dyad. Thereafter, the two sister kinetochores can be seen lying separated on the opposite sides of the dyad. The kinetochore region undergoes a transition from a drumstick shape at metaphase-II to a conic or cylindrical configuration at metaphase-II, but on the other hand, no structural changes are found in the kinetochore region at the onset of anaphase-I. These results show that the kinetochores of the first meiotic chromosomes are structurally different from those of the second meiotic chromosomes in relation to the difference of the behavior between chromosomes in the two successive divisions.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796677

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

In this paper are presented the observations on the microsporogenesis in the diploid (2n= 22) species ofCoffea: C. eugenioidesMoore.C. libericaHiern.,C. KapakataHirsch, andC. racemosaLour. These species displayed a regular meiotic behaviour in most pollen mother cells with formation of 11 bivalents.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796678

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

The mitotic and meiotic chromosome ofPericoma modestawere analyzed. Diploid complement was 2n= 14 and includes the sex-chromosomes which have never been observed in other species of Psychodidae. The heterosomes did not undergo synapsis to form a bivalent at the meiosis, but regularly passed to opposite poles at the first anaphase. This characteristic makes this species comparable to some tipulid flies.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796679

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

Polypedilum nubiferhas four polytene chromosomes (2n= 8). A standard chromosome map of the polytene chromosomes and the limits of 29 alternative sequences are described. Phylogenies for the sequences on arms C, E and G are proposed. Sequences C4, E3, Fl and G1 are apparently quite ancient, and therefore probably ancestral, because of their occurrence in widely separated populations in Australia and Israel. There were no common sequences in arms A1, B1 and D1 but sequences A1, B1 and D1 are the most widespread in Australia. P.nubiferis female heterogametic, females always being heterozygous for a heterodhromatinized differential segment 41cY-dY on arm G. On the basis of the differing frequencies of some of the arm G sequences, it is likely that the sex determining regions are included within the differential 41c-d ends.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796680

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796681

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

Variations on total dry mass concentrations and relative amounts of histones and non-histone proteins were estimated in the chromosome C ofBradysia hygidasalivary glands by means of interferometric, cytophotometric and cytofluorometric procedures.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796682

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

InChamaecyparis lawsonianaParl, the megaspore mother cell (MMC) differentiates in the middle and innermost region of the nucellus as is generally the case in Gymnosperms. During its development the MMC attains a size much larger than that of the surrounding somatic cells and accumulates a considerable amount of food-storage substances. These consist of starch and droplets which could be, at least partly, of lipidic nature. During prophase I the MMC becomes a fully polarized cell since all or almost all the mitochondria are restricted to the chalazal cytoplasm. In the authors' opinion this is determined by the trophically privileged position of the chalazal cytoplasm. The polarization of the chondriome determines the course of the subsequent events in such a way that the meiotic divisions give rise to a linear triad, in which the two micropylar megaspores soon degenerate while the chalazal one inherits all of the mithochondria from the megasporocyte and remains functional. On the other hand the food-storage substances appear more or less uniformly distributed at all megasporogenesis stages.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796683

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

Karyological analyses and rRNA/DNA hybridization experiments were carried out inBellevalia romanaandB. dubia(Liliaceae).B. romana(2n=8) has four short NORs and 3,200 genes for ribosomal RNA; B. dubia (2n=8) has six NORs clearly longer than those ofB. romanaand 9,800 rRNA genes. The gene numbers are calculated on the basis that both species possess 24 × 10−12g/2C nucleus. A correlation between cytological and molecular hybridization results is made.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796684

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

InHeuchera micranthathe anthers are tetrasporangiate and cytokinesis is of simultaneous type. In the majority of the tetrads microspores soon separate from one another but in a few they remain intact. Tetrads with two degenerating and two multinucleate microspores are often observed. In a few tetrads cell walls undergo lysis resulting in a large, spherical 4-nucleate structures. In some anthers, the behaviour of microspores deviates from normal course: (i) Instead of developing into normal pollen grains, the microspores enlarge, their cytoplasm becomes vacuolated and finally they degenerate, (ii) The microspore increases in size and the nucleus undergoes 3 successive divisions giving rise to an 8-nucleate structure. Three nuclei at each pole organize into cells while the remaining 2 lie in the centre. Such elongated microspores resemble organized Polygonum type of female gametophyte. (iii) Spherical, 4- and 8-nucleate microspores showing cruciate arrangement of nuclei are often met with. Disposition of nuclei is comparable to Penea and Plumbago type of female gametophyte. Cell wall formation is, however, not observed.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796685

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor