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11.
During a routine screening of pollen fertility in the n = 2 chromosome race of Haplopappus gracilis, a spineless pollen wall mutation was discovered that renders the otherwise functional pollen grains completely unrecognizable as Compositae pollen. Normal Haplopappus pollen is characterized by an outer layer, the ektexine, consisting of large spines supported by a roof (tectum), which in turn is supported by collumellae that are joined basally. A large cavity (cavea) stretches from aperture to aperture and separates columellae bases from the final ektexine unit, the foot layer. The spines, tectum, columellae, and columellae bases are filled with perforations (internal foramina), while the foot layer is without them. Immediately underlying the foot layer is a thickened, lamellate, disrupted, internal foramina-free second exine layer, the endexine. In contrast, the mutant pollen ektexine is a jumble of components with randomly dispersed spines as the only clearly definable unit. The endexine layer is similar to the endexine in normal pollen. The mutation apparently disrupts only the organization of ektexine units, and mutant pollen appears to be without the caveae and foot layer characteristic of normal pollen. In genetic tests, the mutant allele is recessive. There is a simple Mendelian pattern of inheritance of the mutant gene, and its phenotype is under sporophytic control. 相似文献
12.
Efficient estimation of the prevalence of multiple rare traits 总被引:1,自引:0,他引:1
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Evidence of independent gene duplications during the evolution of archaeal and eukaryotic family B DNA polymerases 总被引:1,自引:0,他引:1
Eukaryotes and archaea both possess multiple genes coding for family B DNA
polymerases. In animals and fungi, three family B DNA polymerases, alpha,
delta, and epsilon, are responsible for replication of nuclear DNA. We used
a PCR-based approach to amplify and sequence phylogenetically conserved
regions of these three DNA polymerases from Giardia intestinalis and
Trichomonas vaginalis, representatives of early-diverging eukaryotic
lineages. Phylogenetic analysis of eukaryotic and archaeal paralogs
suggests that the gene duplications that gave rise to the three replicative
paralogs occurred before the divergence of the earliest eukaryotic
lineages, and that all eukaryotes are likely to possess these paralogs. One
eukaryotic paralog, epsilon, consistently branches within archaeal
sequences to the exclusion of other eukaryotic paralogs, suggesting that an
epsilon-like family B DNA polymerase was ancestral to both archaea and
eukaryotes. Because crenarchaeote and euryarchaeote paralogs do not form
monophyletic groups in phylogenetic analysis, it is possible that archaeal
family B paralogs themselves evolved by a series of gene duplications
independent of the gene duplications that gave rise to eukaryotic paralogs.
相似文献
16.
Jeroen CW Rijk Ad ACM Peijnenburg Peter JM Hendriksen Johan M Van Hende Maria J Groot Michel WF Nielen 《BMC veterinary research》2010,6(1):44
Background
Within the European Union the use of growth promoting agents in animal production is prohibited. Illegal use of natural prohormones like dehydroepiandrosterone (DHEA) is hard to prove since prohormones are strongly metabolized in vivo. In the present study, we investigated the feasibility of a novel effect-based approach for monitoring abuse of DHEA. Changes in gene expression profiles were studied in livers of bull calves treated orally (PO) or intramuscularly (IM) with 1000 mg DHEA versus two control groups, using bovine 44K DNA microarrays. In contrast to controlled genomics studies, this work involved bovines purchased at the local market on three different occasions with ages ranging from 6 to 14 months, thereby reflecting the real life inter-animal variability due to differences in age, individual physiology, season and diet. 相似文献17.
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Recently, a group of diplomonads has been found to use a genetic code in
which TAA and TAG encode glutamine rather than termination. To survey the
distribution of this characteristic in diplomonads, we sought to identify
TAA and TAG codons at positions where glutamine is expected in genes for
alpha-tubulin, elongation factor-1 alpha, and the gamma subunit of
eukaryotic translation initiation factor-2. These sequences show that the
variant genetic code is utilized by almost all diplomonads, with the genus
Giardia alone using the universal genetic code. Comparative phylogenetic
analysis reveals that the switch to this genetic code took place very early
in the evolution of diplomonads and was likely a single event. Termination
signals and downstream untranslated regions were also cloned from three
Hexamita genes. In all three of these genes, the predicted TGA termination
codon was found at the expected position. Interestingly, the untranslated
regions of these genes are high in AT. This is incongruent with the coding
regions, which are comparatively GC-rich.
相似文献
19.
Use of hexamethyldisilazane (HMDS) as a final dehydrating solution provides robust, undistorted secondary electron images of a variety of angiosperm and gymnosperm pollen grains, including those considered to be susceptible to collapse in the scanning electron microscope. Ease of handling, low cost, lack of specialized equipment, minimal expenditure of time, and high rate of success are factors that favor HMDS over other drying agents for preparing pollen grains for scanning' electron microscopy. 相似文献
20.
Aperture morphology of tetrad pollen of Epilobium luteum (Onagraceae: Epilobieae) from three Alaskan collections is highly variable. The first collection appears to lack apertures
altogether and is presumed to consist of immature pollen gains in a genus known to achieve mature size before the apertures
become distinctly protruding. A second collection has tetrads with 3- and 4-apertured grains, the apertures in the latter
are often irregularly spaced and not in apposition with the apertures of neighboring members. The third collection consists
of the more typical 3-apertured members that characterize the majority of Epilobium pollen grains. In all of these collections individual pollen grains (monads) are interspersed among the tetrads. The variations
in the number of apertures emphasize the importance of having a comprehensive understanding of the stage of development of
the pollen (taxon) examined when describing pollen collections. In the first collection this would mean the recognition that
in Onagraceae apertures occur in the later stages of microspore ontogeny. In the latter two collections a thorough background
of the literature of the pollen morphology on this largest Onagraceae taxon is useful for the understanding of the significance
of a range of aperture numbers on Epilobium pollen grains. 相似文献