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91.
92.
Nader Hassan Kurt Mereiter Gabor Molnar Markus Valtiner Wolfgang Linert 《Inorganica chimica acta》2008,361(5):1291-1297
A series of 1-(tetrazol-1-yl)alkanes [ntz] with n = 1-4 were synthesised as ligands for iron(II) spin crossover complexes. Within this series 1-(tetrazol-1-yl)butane [4tz] was prepared for the first time, whereas 1-(tetrazol-1-yl)methane [1tz], 1-(tetrazol-1-yl)ethane [2tz], 1-(tetrazol-1-yl)propane [3tz] and the [hexakis(ntz)iron(II)]bis(tetrafluoroborate) complexes were prepared according to the literature. Aiming for a comparative study we characterized all four compounds by XRPD, magnetic susceptibility measurements, 57Fe-Moessbauer spectroscopy and IR spectroscopy. [Fe(4tz)6](BF4)2 yielded appropriate single crystals and an X-ray structure of the new compound [Fe(4tz)6](BF4)2 is presented. The magnetic and structural properties of all [Fe(ntz)6](BF4)2 are compared and discussed. 相似文献
93.
《Cell cycle (Georgetown, Tex.)》2013,12(3):305-314
During meiosis, crossover recombination is tightly regulated. A spatial patterning phenomenon known as interference ensures that crossovers are well-spaced along the chromosomes. Additionally, every pair of homologs acquires at least one crossover. A third feature, crossover homeostasis, buffers the system such that the number of crossovers remains steady despite decreases or increases in the number of earlier recombinational interactions. Here we summarize recent work from our laboratory supporting the idea that all 3 of these aspects are intrinsic consequences of a single basic process and suggesting that the underlying logic of this process corresponds to that embodied in a particular (beam-film) model. 相似文献
94.
Nader Hassan Frank Kubel Azzedine Bousseksou Roman Bo?a 《Inorganica chimica acta》2009,362(10):3629-700
Two new 1-(tetrazol-1-yl)cycloalkanes [Cntz] with n = 5 and 6 were synthesised as ligands for iron(II) spin crossover complexes. Just recently, the [Fe(C3tz)6](BF4)2 showed that the rigid cyclopropyl-substituent of the tetrazole yielded a rather abrupt and complete spin transition at T½ ≈ 190 K [1]. Aiming for a deeper insight into the factors governing the spin transition behavior such as abruptness and spin transition temperature we synthesized the two new homologous complexes [Fe(C5tz)6](BF4)2 and [Fe(C6tz)6](BF4)2 which were characterized by XRPD, magnetic susceptibility measurements, DSC, 57Fe-Mössbauer, UV-Vis-NIR and MIR spectroscopy. The magnetic and structural properties of both [Fe(Cntz)6](BF4)2 with n = 5 and 6 are also compared with the [Fe(C3tz)6](BF4)2 and its structural peculiarities are discussed. 相似文献
95.
A. P. Grieve 《Biometrical journal. Biometrische Zeitschrift》1987,29(7):771-775
In the analysis of a two-period crossover study Grizzle (1965) suggests that, if a preliminary test for a period by treatment interaction (residual effect, carryover effect) is significant at the 10 % level, the direct effects of the treatments should be compared by performing a t-test on the data from the first period only. In this note it is shown that under Grizzle's model the comparison of the direct treatment effects is equivalent to a Behrens-Fisher problem. Depending on one's viewpoint–Bayesian, fiducial, or sampling theory–different solutions are possible. The solutions are illustrated using three well-known data sets. 相似文献
96.
Little is known about the factors determining the location and activity of the rapidly evolving meiotic crossover hotspots that shape genome diversity. Here, we show that several histone modifications are enriched at the active mouse Psmb9 hotspot, and we distinguish those marks that precede from those that follow hotspot recombinational activity. H3K4Me3, H3K4Me2 and H3K9Ac are specifically enriched in the chromatids that carry an active initiation site, and in the absence of DNA double-strand breaks (DSBs) in Spo11−/− mice. We thus propose that these marks are part of the substrate for recombination initiation at the Psmb9 hotspot. In contrast, hyperacetylation of H4 is increased as a consequence of DSB formation, as shown by its dependency on Spo11 and by the enrichment detected on both recombining chromatids. In addition, the comparison with another hotspot, Hlx1, strongly suggests that H3K4Me3 and H4 hyperacetylation are common features of DSB formation and repair, respectively. Altogether, the chromatin signatures of the Psmb9 and Hlx1 hotspots provide a basis for understanding the distribution of meiotic recombination. 相似文献
97.
During meiosis, homologous chromosomes (homologs) pair and undergo genetic recombination via assembly and disassembly of the synaptonemal complex. Meiotic recombination is initiated by excess formation of DNA double-strand breaks (DSBs), among which a subset are repaired by reciprocal genetic exchange, called crossovers (COs). COs generate genetic variations across generations, profoundly affecting genetic diversity and breeding. At least one CO between homologs is essential for the first meiotic chromosome segregation, but generally only one and fewer than three inter-homolog COs occur in plants. CO frequency and distribution are biased along chromosomes, suppressed in centromeres, and controlled by pro-CO, anti-CO, and epigenetic factors. Accurate and high-throughput detection of COs is important for our understanding of CO formation and chromosome behavior. Here, we review advanced approaches that enable precise measurement of the location, frequency, and genomic landscapes of COs in plants, with a focus on Arabidopsis thaliana. 相似文献
98.
Michaelyn A. Hartmann 《Fly》2017,11(4):253-259
Drosophila melanogaster chromosome 4 is an anomaly because of its small size, chromatin structure, and most notably its lack of crossing over during meiosis. Earlier ideas about the absence of crossovers on 4 hypothesize that these unique characteristics function to prevent crossovers. Here, we explore hypotheses about the absence of crossovers on 4, how these have been addressed, and new insights into the mechanism behind this suppression. We review recently published results that indicate that global crossover patterning, in particular the centromere effect, make a major contribution to the prevention of crossovers on 4. 相似文献
99.
100.
Biogeographically distinct controls on C3 and C4 grass distributions: merging community and physiological ecology 下载免费PDF全文