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61.
Restriction mapping is used to estimate nucleotide sequence polymorphism
when the regions to be studied are too long or too numerous to be
sequenced. Restriction mapping is less costly than DNA sequencing, but it
does not allow direct measurement of underlying nucleotide polymorphism. It
is therefore useful to be able to estimate underlying nucleotide
polymorphism from observations of polymorphism in restriction maps, as this
offers some of the resolution afforded by DNA sequencing at a reduced cost.
Previous estimators of underlying nucleotide polymorphism have assumed that
each restriction-enzyme- binding site contains, at most, a single
polymorphic nucleotide position (the low-polymorphism-frequency
assumption), and this assumption has placed an upper limit on the level of
polymorphism that can be resolved by these estimators. The present study
documents an estimator which allows relaxation of this assumption. The new
estimator more accurately estimates underlying nucleotide polymorphism when
the polymorphism level is high enough to falsify the low-polymorphism-
frequency assumption. The new estimator therefore yields good results for
data sets that are too divergent for analysis by present methods.
相似文献
62.
The biogeochemistry of basic cations in two forest catchments with contrasting lithology in the Czech Republic 总被引:2,自引:0,他引:2
PAVEL KRÁM JAKUB HRUŠKA BRIAN S. WENNER CHARLES T. DISCOLL CHRIS E. JOHNSON 《Biogeochemistry》1997,37(2):173-202
The biogeochemistry of Ca, Mg, K, and Nawere investigated in two forested catchments in theCzech Republic, one underlain by leucogranite, theother by serpentinite. High weathering rates at theserpentinite site at Pluhv Bor resultedin Mg2+ as the dominant cation on the soilexchange complex and in drainage water. Other basiccations (Ca2+, K+, Na+) showedrelatively low concentrations and outflow instreamwater. The catchment exhibited high basesaturation in mineral soils (>70%), and nearneutral soil and stream pH, despite elevated inputsof acidic deposition. Slow growth of Norway spruceat Pluhv Bor may be caused by K deficiency, Mgoversupply and/or Ni toxicity. In contrast, thegranitic site at Lysina showed low concentrations ofbasic cations on the soil exchange complex and instreamwater. Soil and drainage water at Lysina werehighly impacted by acidic deposition. Soil pH wasextremely acidic (<4.5) throughout the soilprofile, and the base saturation of the mineral soilwas very low (<5%). Supplies of basic cationsfrom atmospheric deposition and soil processes wereless than inputs of SO2-
4 on anequivalence basis, resulting in low pH and highconcentrations of total Al in drainage water. Needle yellowing in Norway spruce was possibly theresult of Mg deficiency at Lysina. Because of theirextremely different lithologies, these catchmentsserve as valuable end-members of ecosystemsensitivity to elevated levels of acidicdeposition. 相似文献
63.
ZDENEK IKA 《The Journal of eukaryotic microbiology》1972,19(2):275-280
SYNOPSIS. In an electron microscope study of the neogregarine Farinocystis tribolii Weiser 1953 in the fat body of the larvae of the flour beetle Tribolium castaneum , empty oocysts and adjacent sporozoites of the gregarine were found. The empty oocysts contained host cell cytoplasm, a residuum only slightly larger than that in mature oocysts, and some remnants of the oocyst membrane pressed tightly against the inner surface of the wall. Apparently normal sporozoites were found near the empty oocysts and no damaged ones were seen. It is assumed that the sporozoites go on developing in the host, i.e., that autoinfection takes place. 相似文献
64.
ANETT HARSÁNYI MARGARETA RYBERG MATS X. ANDERSSON KÁROLY BÓKA LAJOS LÁSZLÓ GERGELY BOTOND BÉLA BÖDDI RICHARD GÁBORJÁNYI 《Molecular Plant Pathology》2006,7(6):533-541
To understand the phenomenon by which infection of seed-transmitted Barley stripe mosaic virus (BSMV) alters membrane structures and inhibits protochlorophyllide biosynthesis of dark-grown barley ( Hordeum vulgare L.) plants, we analysed the presence of NADPH:protochlorophyllide oxidoreductase (POR, EC 1.3.1.33) and the galactolipid content and fatty acid composition. The amount of POR in etioplasts of infected leaves, compared with non-infected leaves, was reduced, as measured by immunoelectron microscopy and Western blot. These results are in agreement with the previously described reduction of the ratio of the photoactive 650 nm to non-photoactive 630 nm absorbing protochlorophyllide forms ( Harsányi et al. , 2002 . Physiol. Plant 114 , 149–155). The galactolipid content was lower in infected leaves. Monogalactosyl-diacylglycerol (MGDG) content was reduced to 40% and digalactosyl-diacylglycerol to 55% of control plants on a fresh weight basis. In infected plants, the proportion of linolenic acid decreased in both galactolipids. The lower amount of highly unsaturated fatty acids and the reduced abundance of MGDG correlated well with the previously detected reduction in the membrane ratio of prolamellar body (PLB) to prothylakoid ( Harsányi et al. , 2002 . Physiol. Plant 114 , 149–155). The reduced amount of POR and the above described alterations in the lipid composition resulted in a disturbed structure of PLBs. As a consequence, pigment synthesis and the greening process were inhibited in infected cells, in turn explaining the appearance of chlorotic stripes of BSMV-infected barley leaves. Our results show that BSMV infection can be detected at a very early stage of leaf development. 相似文献
65.
66.
67.
不同退化阶段高寒草甸土壤化学计量特征 总被引:13,自引:1,他引:13
为了阐明不同退化阶段高寒草甸土壤的化学计量特征,沿着高寒草甸退化的梯度选取了原生嵩草草甸、轻度退化草甸和严重沙化草甸,测定了高寒草甸退化过程中不同深度土壤的有机碳、全氮、全磷和全钾含量。结果表明:随着高寒草甸的退化,0~100cm土壤的有机碳、全氮、全磷和全钾含量以及碳氮比、碳磷比、碳钾比、氮磷比、氮钾比和磷钾比均呈降低趋势,且土壤有机碳对高寒草甸退化的敏感性最高,全氮、全磷和全钾的敏感性依次降低,表层20cm的土壤有机碳和全氮可作为表征高寒草甸退化程度最敏感的土壤养分指标。另外,随着草甸的退化,土壤的有机碳、全氮、全磷和全钾含量及其化学计量比的垂直分布明显不同:随着土壤深度的增加,原生嵩草草甸和轻度退化草甸的土壤有机碳、全氮和全磷含量以及碳氮比、碳磷比、碳钾比、氮磷比、氮钾比和磷钾比在0~40cm范围内锐减,在40cm以下缓慢降低并趋于稳定;而沙化草甸土壤的有机碳、全氮、全磷和全钾及其化学计量比随着土壤深度的增加保持不变。 相似文献
68.
红细胞在钙离子和离子载体A23187作用下的流变特性研究 总被引:1,自引:0,他引:1
用新激光衍射法研究了钙离子及离子载体A23187对红细胞流变特性的影响.用不同浓度的钙离子及离子载体A23187分别处理红细胞后,测量其取向指数和小变形指数.结果表明离子载体A23187较细胞外钙离子浓度对红细胞流变特性的影响更大.而且,最大取向指数和最大小变形指数随着钙离子及离子载体A23187浓度的增加而降低.离子载体A23187浓度增加导致红细胞变形能力明显降低. 相似文献
69.
KA Hyndman DH Evans 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2009,152(1):58-65
We recently determined that rapid changes in environmental salinity alter endothelin-1 (EDN1) mRNA levels in the euryhaline killifish, Fundulus heteroclitus, so we hypothesized that EDN1 may be a local regulator of gill ion transport in teleost fishes. The purpose of the present study was to examine the effects of changes in environmental salinity on the gill endothelin receptors: EDNRA, EDNRB, and EDNRC. Using quantitative real-time PCR, we determined that after a fresh water (FW) to seawater (SW) transfer, there is a two to threefold increase in gill EDNRA and EDNRB mRNA levels. Likewise, we found a two to three fold increase in gill EDNRA and EDNRB protein concentration. In addition, killifish that have acclimated to FW for 30 days had significantly lower EDNRA mRNA and protein levels than SW killifish. ENDRA were immunolocalized to the mitochondrion-rich cells of the killifish gill, suggesting that EDN1 signaling cascades may affect MRC function. EDNRB were found throughout the gill vasculature and on lamellar pillar cells. We previously immunolocalized EDN1 to the pillar cell suggesting that EDN1 acts as an autocrine signaling molecule and potentially regulates pillar cell tone and lamellar perfusion. We conclude that EDN1 is physiologically active in the teleost gill, and regulated by environmental salinity. Future functional studies examining the physiological role of this system are necessary to completely understand EDN1 in the fish gill. 相似文献
70.
The mutation rates of di-, tri- and tetranucleotide repeats in Drosophila melanogaster 总被引:3,自引:1,他引:3
Schug MD; Hutter CM; Wetterstrand KA; Gaudette MS; Mackay TF; Aquadro CF 《Molecular biology and evolution》1998,15(12):1751-1760
In a recent study, we reported that the combined average mutation rate of
10 di-, 6 tri-, and 8 tetranucleotide repeats in Drosophila melanogaster
was 6.3 x 10(-6) mutations per locus per generation, a rate substantially
below that of microsatellite repeat units in mammals studied to date (range
= 10(-2)-10(-5) per locus per generation). To obtain a more precise
estimate of mutation rate for dinucleotide repeat motifs alone, we assayed
39 new dinucleotide repeat microsatellite loci in the mutation accumulation
lines from our earlier study. Our estimate of mutation rate for a total of
49 dinucleotide repeats is 9.3 x 10(-6) per locus per generation, only
slightly higher than the estimate from our earlier study. We also estimated
the relative difference in microsatellite mutation rate among di-, tri-,
and tetranucleotide repeats in the genome of D. melanogaster using a method
based on population variation, and we found that tri- and tetranucleotide
repeats mutate at rates 6.4 and 8.4 times slower than that of dinucleotide
repeats, respectively. The slower mutation rates of tri- and
tetranucleotide repeats appear to be associated with a relatively short
repeat unit length of these repeat motifs in the genome of D. melanogaster.
A positive correlation between repeat unit length and allelic variation
suggests that mutation rate increases as the repeat unit lengths of
microsatellites increase.
相似文献