ISSN:0008-7114    

DOI:10.1080/00087114.1984.10797681

出版商:Taylor & Francis    

年代:1984

数据来源: Taylor

摘要:

Chromosome I ofTriturus cristatusis readily distinguished after Giemsa C-banding by the heterochromatic region on its long arm. The heteromorphic banding pattern within this region reported previously was found sporadically but not reproducibly. Mortality of half the tailbud embryos from artificial spawnings is confirmed and is probably true for naturally spawned eggs raised in the laboratory, but the survivors often show an unequal sex ratio. These results suggest crested newts have evolved from a genotypic to an environmental control of sex determination, so that chromosome I may be considered as a relict sex chromosome.

ISSN:0008-7114    

DOI:10.1080/00087114.1984.10797682

出版商:Taylor & Francis    

年代:1984

数据来源: Taylor

摘要:

The chromosome morphology of four populations ofDugesia gonoce-phalas.l. from various European localities is described. Three populations (S1, V26 and V35) showed diploid complements of 16 metacentric chromosomes, whereas one population (V28) has a triploid complement of 24 meta- and submetacentric chromosomes. The karyotypes of the populations show small variation of chromosome length and centromere position, which do not enable the identification of individual chromosomes. For a statistical approach of this problem, the 95% confidence limits of relative length and centromeric index were calculated for each chromosome and set out in two dimensional scatter diagram. It is argued that in cases where chromosomes decrease gradually in relative length and show similar centromeric indices, matching of chromosomes in pairs is statistically unsound. Chromosome differentiation techniques were introduced to obtain characteristic banding patterns for chromosome recognition. Tentative results obtained with the BSG-technique showed clear C-bands at the telomeres and centromere regions of some chromosomes. Silver (Ag-As) staining demonstrated the presence of Ag-NORs in two chromosomes of one of the populations. Quinacrine staining of squashed blastemas revealed rather uniform fluorescence intensity at all chromosomes.

ISSN:0008-7114    

DOI:10.1080/00087114.1984.10797683

出版商:Taylor & Francis    

年代:1984

数据来源: Taylor

摘要:

The ultrastructure of the development of the pollen grain is described from the first meiotic division to the binucleate phase. The first meiotic division is synchronous in all the microspore mother cells and cytomictic channels still join their protoplasts together. The tapetal cells, their individual walls now degraded, almost completely surround but do not touch the microspore mother cells. In the latter the cytoplasm can be divided into two zones. The central zone, the division zone, is occupied primarily by ribosomes, smooth ER and dictyosomes. In the outer zone lie all the other usual organelles and small vacuoles. The plastids are partly surrounded by ER. In interphase the cytomictic channels close and the second division is not synchronous. Autophagic vacuoles form, apparently destroying some of the ribosomes. The callose walls form after meiosis and the tapetum degenerates. The primexine, which appears to have a polysaccharide skeleton, begins to form between the plasmalemma and the callose wall. The callose wall then dissolves, the pores begin to form, sporopollenin begin to accumulate and the exine is completed. The spores then pass through a stage of vacuolation and of amylogenesis and loss of starch. At mitosis the new wall separating the vegetative and generative cells is formed, and it is not perforated by plasmodesmata. The pore structure is now completed and autophagic vacuoles destroy further regions both of the vegetative cell's cytoplasm and to a lesser extent that of the generative cell. New cytoplasm is successively formed, together with another wave of amylogenesis and loss of starch; these two processes occur simultaneously with the dehydration of the grain as the pollen structure matures.

ISSN:0008-7114    

DOI:10.1080/00087114.1984.10797684

出版商:Taylor & Francis    

年代:1984

数据来源: Taylor

摘要:

In this paper, the authors analyse the chromosomes of a field population ofBilobella aurantiacafrom Sainte Baume (Southern France). They display a low polymorphism and high content of heterochromatin, in contrast to populations of central Spain. The observation of ectopic pairing suggests the presence of two types of heterochromatin: telomeric heterochromatin is frequently involved in ectopic pairing, while centromeric heterochromatin never is. The amount of heterochromatin and the extent of polymorphism seem to vary in opposite directions from one population to an other according to general climatic conditions: the existence of two different adaptative strategies is proposed on this basis.

ISSN:0008-7114    

DOI:10.1080/00087114.1984.10797685

出版商:Taylor & Francis    

年代:1984

数据来源: Taylor

摘要:

The monospecific genusBaeticais characterized by extensive amounts of C-heterochromatin, placed on M3, M4and M5chromosomes, as large c-blocks or some intestinal C-bands. The only karyotypic variation founded among the analysed individuals of this genus is a considerable degree of polymorphism for the presence, placement and amount of C-band positive chromatin. These differences seem to be related to the additions of constitutive heterochromatin, which probably constitutes the major mode of karyotypic change occurring in the evolution ofB. ustulata.Significative differences exist between the observed frequencies of the various genotypes and the Hardy-Weinberg expectations, in both M4and M5chromosome pairs.

ISSN:0008-7114    

DOI:10.1080/00087114.1984.10797686

出版商:Taylor & Francis    

年代:1984

数据来源: Taylor

摘要:

Many discussions about taxonomic significance of dolipore/parenthe-some ultrastructure have been published, during the last few years. However, the problem is difficult because, in the majority of Basidiomycetes, the real function of the pore cap is undecided. Our research shows that the dolipore/parenthesome ultrastructure ofTremella mesentericaFries, varies according to its location, either in the secondary micelium hyphae, or at the basidum base, or in the conidiophore hyphae. In addition, the conidiophore hyphae extremities, when dividing to form conidia, form a passage that is always without a parenthesome. This variability suggests that dolipore-/parenthesome morphology is connected with different functions, according to its location.

ISSN:0008-7114    

DOI:10.1080/00087114.1984.10797687

出版商:Taylor & Francis    

年代:1984

数据来源: Taylor

摘要:

Scyllina signatipennisis a Gomphocerine grasshopper whose male karyotype of 23 telocentric chromosomes includes 11 autosomal pairs (3 long: L1-L3; 5 medium-sized: M4-M8; short: 3 S9-S11) and an X-chromosome. Males show an extreme pattern of proximal chiasma localization during meiosis which is characterized by a preleptotenic contraction stage followed by an unravelling stage which precedes a typical leptotene. The nucleus then enters a prolonged diffuse stage that comprises most of zygotene and pachytene. Post-diffuse nuclei represent an intermediate stage between pachytene and diplotene and at this time some homologous pairing is evident. Usually, only one chiasma per bivalent is observed and chiasma frequency per cell ranges from 11.00 to 11.15. An analysis of the percentage of pairing in post-diffuse nuclei suggests that incomplete pairing cannot be the cause of chiasma localization in this species. A role for the diffuse stage in determining chiasma localization is suggested since other species with localization also show a prolonged diffuse stage which replaces conventional zygotene and pachytene. A further interesting feature of meiosis inSc. signatipennisis the behaviour of the X univalent which is negatively heteropycnotic during most of the diffuse stage suggesting that it could be involved in transcriptional activities. It also showed a high frequency of neocentric activity in metaphase I in most of the individuals. This was correlated with stable equatorial orientation whereas in individuals in which neocentric activity was not apparent, the X usually migrated precociously to one of the spindle poles.

ISSN:0008-7114    

DOI:10.1080/00087114.1984.10797688

出版商:Taylor & Francis    

年代:1984

数据来源: Taylor

摘要:

From counts of spermatocyte and oocyte bivalents and of mitotic chromosomes we have determined the haploid numbern= 13 and the diploid number 2n= 26 for the speciesHydroides elegans.No sex-differentiated chromosome was found. A peculiar stretch between daughter kinetochores was observed at mitotic premeta-phase stage.

ISSN:0008-7114    

DOI:10.1080/00087114.1984.10797689

出版商:Taylor & Francis    

年代:1984

数据来源: Taylor

摘要:

Pollen germination and pollen tube growth were studied by fluorescence technique in pistil ofCrocus sativusand C.thomasiiafter intra- and interspecific pollinations. The results indicated thatC. sativuspollen germinates in low percentage in all the stigmas and some pollen tubes grow down to the ovules. In both theCrocusspecies the pollen tube growth is accompanied by anormalities of pollen tube behaviour and its tip aspect. Since most of these abnormalities are found in all the pistil parts it was not possible to correlate them with incompatibility in the studied plants.

ISSN:0008-7114    

DOI:10.1080/00087114.1984.10797690

出版商:Taylor & Francis    

年代:1984

数据来源: Taylor