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21.
Meiotic Recombination Initiated by a Double-Strand Break in Rad50Δ Yeast Cells Otherwise Unable to Initiate Meiotic Recombination 下载免费PDF全文
Meiotic recombination in Saccharomyces cerevisiae is initiated by double-strand breaks (DSBs). We have developed a system to compare the properties of meiotic DSBs with those created by the site-specific HO endonuclease. HO endonuclease was expressed under the control of the meiotic-specific SPO13 promoter, creating a DSB at a single site on one of yeast's 16 chromosomes. In Rad(+) strains the times of appearance of the HO-induced DSBs and of subsequent recombinants are coincident with those induced by normal meiotic DSBs. Physical monitoring of DNA showed that SPO13::HO induced gene conversions both in Rad(+) and in rad50Δ cells that cannot initiate normal meiotic DSBs. We find that the RAD50 gene is important, but not essential, for recombination even after a DSB has been created in a meiotic cell. In rad50Δ cells, some DSBs are not repaired until a broken chromosome has been packaged into a spore and is subsequently germinated. This suggests that a broken chromosome does not signal an arrest of progression through meiosis. The recombination defect in rad50Δ diploids is not, however, meiotic specific, as mitotic rad50 diploids, experiencing an HO-induced DSB, exhibit similar departures from wild-type recombination. 相似文献
22.
The genetic basis of phenotypic convergence in beach mice: similar pigment patterns but different genes 总被引:2,自引:0,他引:2
Steiner CC Römpler H Boettger LM Schöneberg T Hoekstra HE 《Molecular biology and evolution》2009,26(1):35-45
Convergent evolution is a widespread phenomenon seen in diverseorganisms inhabiting similar selective environments. However,it is unclear if similar phenotypes are produced by the sameor different genes and mutations. Here we analyze the molecularmechanisms underlying convergent pigment pattern among subspeciesof the beach mouse (Peromyscus polionotus) inhabiting the Gulfand Atlantic coasts of Florida. In these two geographic regions,separated by more than 300 km, "beach mice" have lighter coloredcoats than do their mainland counterparts, produced by naturalselection for camouflage against the pale coastal sand dunes.We measured color pattern in eight beach mouse subspecies andshowed that three of the Gulf Coast subspecies are more phenotypicallysimilar to an Atlantic coast subspecies than to their Gulf Coastneighbors. However, light-colored beach mice do not form a monophyleticgroup. Previous results implicated a single derived amino acidchange in the melanocortin-1 receptor (Mc1r) as a major contributorto pigment pattern in the Gulf Coast beach mice; despite phenotypicsimilarities, the derived Mc1r allele was not found in the Atlanticcoast beach mouse populations. Here we show that Atlantic coastbeach mice have high levels of Mc1r polymorphism but they lackunique alleles. Functional assays revealed that single aminoacid mutations segregating in Atlantic coast beach mice do notcause any change in Mc1r activity compared with the activityof Mc1r from dark-colored mice. These joint results show thatconvergent pigment patterns in recently diverged beach mousesubspecies—whose developmental constraints are presumablysimilar—have evolved through a diversity of genetic mechanisms. 相似文献
23.
Dirk?T.?Hoekstra Heinrich?Volschenk Michelle?Collins Lynn?D.?McMasterEmail author 《Journal of applied phycology》2011,23(4):777-787
The presence of the anaerobic spore former Clostridium in Arthrospira platensis destined for human consumption is generally not assessed during quality assurance procedures. As this nutraceutical is administered
as complementary medicine to the immunocompromised, this study aimed to investigate the presence of these potential pathogens.
Anaerobic counts performed on tablets from a single manufacturer indicated an excess of 105 CFU/endospores g−1 tablet for three different A. platensis batches. Tests for coliforms for use as “indicators” of pathogens in the tablets were negative. Using classic culture techniques,
five species of Clostridium were isolated. Subsequent use of PCR-denaturing gradient gel electrophoresis (DGGE) fingerprinting of tablets showed a divergent
microbial population, with a predominance of anaerobic endospore formers, including Clostridium. Sequencing of a 1.5 kb 16S rDNA clone library and phylogenetic analyses of prominent operational taxonomic units confirmed
the presence of an additional five Clostridium spp. and other genera in the tablets. A composite molecular ladder, using 16S rRNA DGGE amplicons of 17 representative bacterial
species was constructed to assist in identifying anaerobes present in tablets sourced from three different A. platensis manufacturers. Results indicated that commercial A. platensis preparations were contaminated with potentially hazardous clostridia and other anaerobic species. Results suggest that certain
commercial A. platensis preparations require stringent microbial quality assurance measures to ensure safe use as a nutraceutical for the immunocompromised
and the general public. 相似文献
24.
Identifying adaptively important loci in recently bottlenecked populations – be it natural selection acting on a population following the colonization of novel habitats in the wild, or artificial selection during the domestication of a breed – remains a major challenge. Here we report the results of a simulation study examining the performance of available population-genetic tools for identifying genomic regions under selection. To illustrate our findings, we examined the interplay between selection and demography in two species of Peromyscus mice, for which we have independent evidence of selection acting on phenotype as well as functional evidence identifying the underlying genotype. With this unusual information, we tested whether population-genetic-based approaches could have been utilized to identify the adaptive locus. Contrary to published claims, we conclude that the use of the background site frequency spectrum as a null model is largely ineffective in bottlenecked populations. Results are quantified both for site frequency spectrum and linkage disequilibrium-based predictions, and are found to hold true across a large parameter space that encompasses many species and populations currently under study. These results suggest that the genomic footprint left by selection on both new and standing variation in strongly bottlenecked populations will be difficult, if not impossible, to find using current approaches. 相似文献
25.
Tanja G. M. Vrijkotte Bert-Jan H. van den Born Christine M. C. A. Hoekstra Maaike G. J. Gademan Manon van Eijsden Susanne R. de Rooij Marcel T. B. Twickler 《PloS one》2015,10(9)
Background
In adults, increased sympathetic and decreased parasympathetic nervous system activity are associated with a less favorable metabolic profile. Whether this is already determined at early age is unknown. Therefore, we aimed to assess the association between autonomic nervous system activation and metabolic profile and its components in children at age of 5–6 years.Methods
Cross-sectional data from an apparently healthy population (within the ABCD study) were collected at age 5–6 years in 1540 children. Heart rate (HR), respiratory sinus arrhythmia (RSA; parasympathetic activity) and pre-ejection period (PEP; sympathetic activity) were assessed during rest. Metabolic components were waist-height ratio (WHtR), systolic blood pressure (SBP), fasting triglycerides, glucose and HDL-cholesterol. Individual components, as well as a cumulative metabolic score, were analyzed.Results
In analysis adjusted for child’s physical activity, sleep, anxiety score and other potential confounders, increased HR and decreased RSA were associated with higher WHtR (P< 0.01), higher SBP (p<0.001) and a higher cumulative metabolic score (HR: p < 0.001; RSA: p < 0.01). Lower PEP was only associated with higher SBP (p <0.05). Of all children, 5.6% had 3 or more (out of 5) adverse metabolic components; only higher HR was associated with this risk (per 10 bpm increase: OR = 1.56; p < 0.001).Conclusions
This study shows that decreased parasympathetic activity is associated with central adiposity and higher SBP, indicative of increased metabolic risk, already at age 5–6 years. 相似文献26.
Michael D. Jennings Jonathan Hoekstra Jonathan Higgins Timothy Boucher 《Biodiversity and Conservation》2008,17(4):833-840
In conservation planning, species richness and species endemism are the most often used metrics for describing the biodiversity
importance of areas. However, when it comes to prioritizing regions for conservation actions these measures alone are insufficient
because they do not reveal how similar or different the actual composition of species may be from one area to another. For
comparative analysis an additional useful metric would be one that indicates the degree to which the species assemblage in
one area is also represented in—or is distinct from—species assemblages of other areas. Here we describe a method for quantifying
the compositional representativeness of species assemblages among geographic regions. The method generates asymmetric pairwise
similarity coefficients that are then used to calculate separate measures for the representativeness and the distinctiveness
of species assemblages in the regions being compared. We demonstrate the method by comparing fish communities among freshwater
ecoregions of the Mississippi Basin, and then among smaller hydrological units within two individual freshwater ecoregions.
At both scales of analysis, our measures of representativeness and distinctiveness reveal patterns of fish species composition
that differ from patterns of species richness. This information can enhance conservation planning processes by ensuring that
priority-setting explicitly consider the most representative and distinctive species assemblages. 相似文献
27.
Claessens MM van Oort BF Leermakers FA Hoekstra FA Cohen Stuart MA 《Biophysical journal》2004,87(6):3882-3893
The swelling behavior of charged phospholipids in pure water is completely different from that of neutral or isoelectric phospholipids. It was therefore suggested in the past that, instead of multilamellar phases, vesicles represent the stable structures of charged lipids in excess water. In this article, we show that this might indeed be the case for dioleoylphosphatidylglycerol and even for dioleoylphosphatidylcholine in certain salts. The size of the vesicles formed by these lipids depends on the phospholipid concentration in a way that has been predicted in the literature for vesicles of which the curvature energy is compensated for by translational entropy and a renormalization of the bending moduli (entropic stabilization). Self-consistent field calculations on charged bilayers show that the mean bending modulus kc and the Gaussian bending modulus k have opposite sign and /k/>kc, especially at low ionic strength. This has the implication that the energy needed to curve the bilayer into a closed vesicle Eves=4pi(2kc+k) is much less than one would expect based on the value of kc alone. As a result, Eves can relatively easily be entropically compensated. The radii of vesicles that are stabilized by entropy are expected to depend on the membrane persistence length and thus on kc. Experiments in which the vesicle size is studied as a function of the salt and the salt concentration correlate well with self-consistent field predictions of kc as a function of ionic strength. 相似文献
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Joya E. Nahon Menno Hoekstra Vanessa van Harmelen Patrick C.N. Rensen Ko Willems van Dijk Sander Kooijman Miranda Van Eck 《生物化学与生物物理学报:疾病的分子基础》2019,1865(2):494-501