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131.
A nearly universal feature of intron sequences is that even closely related
species exhibit a large number of insertion/deletion differences. The goal
of the analysis described here is to test whether the observed pattern of
insertion/deletion events in the genealogy of the myosin alkali light chain
(Mlc1) gene is consistent with neutrality, and if not, to determine the
underlying forces of evolutionary change. Mlc1 pre-mRNA is alternatively
spliced, and one constraint is that signals necessary for
tissue-specificity of directed splicing must be conserved. If the total
length of an intron is functionally constrained, then the distribution of
indels on branches of the gene genealogy should reflect a departure from
randomness. Here we perform a phylogenetic analysis, inferring ancestral
states wherever possible on a phylogeny of 29 alleles of Mlc1 from six
species of Drosophila. Observed patterns of indels on the genealogy were
compared to those from simulated data, with the result that we cannot
reject the null hypothesis of neutrality. A clear departure from a neutral
prediction was seen in the excess folding free energy predicted for the
introns flanking the alternatively spliced exon. Relative rate tests also
suggest a retardation in the rate of Mlc1 sequence evolution in the
simulans clade.
相似文献
132.
Chemical characterization of exopolysaccharides from the marine fouling diatom amphora coffeaeformis
Amphora coffeaeformis cells were grown in batch cultures under continuous illumination at 18°C for 10 d. Algal cells were removed by centrifugation, lyophilized and used for the extraction of exopolysaccharides using either 0.05 M EDTA, 1 M NaOH or 1.5 M NaCl. The 1.5 M NaCl treatment removed most exopolysaccharides. Glucose (81%) was the most abundant monosaccharide in the exopolysaccharides. The chemical composition data suggest that the exopolymers were acidic sulphated polysaccharides containing high concentrations of pyruvate (22%) and uronic acids (18%). These polysaccharides may play an important role in metal complexation and protection from desiccation in A. coffeaeformis. 相似文献
133.
Shear deactivation of cellulase and its major component enzymes, viz., exoglucanase (exo-1,4-beta-D-glucan-4-cellobiohydrolase), endoglucanase (endo-1,4-beta-D-glucanhydrolase), and 1,4-beta-glucosidase, was carried out by exposing cellulase to shear in a mechanically agitated reactor in the presence as well as in the absence of the substrate cellulose. Cellulase was found to undergo deactivation when subjected to shear, and the extent of deactivation increased with increasing speed of agitation. Among the three major component enzymes of cellulase, exoglucanase showed rapid deactivation and contributed the most to cellulase deactivation. The presence of a substrate did not affect the deactivation of cellulase. 相似文献
134.
135.
Killer toxin activity of Pichia anomala WC65 appeared fungicidal for P. bimundalis WC38 and fungistatic for Candida albicans RC1. Inhibitory activity against sensitive C. albicans showed a linear relationship between toxin concentrations and the inverse of the reduced growth rates. The plot of toxin concentrations against growth rates was hyperbolic, as is characteristic of saturation kinetics. Sensitivity of C. albicans to the toxin decreased with increased cell age. The measurement of growth rate reduction provided a simple and accurate method for quantitation of toxin. 相似文献
136.
A likelihood approach for comparing synonymous and nonsynonymous nucleotide substitution rates, with application to the chloroplast genome 总被引:29,自引:24,他引:5
A model of DNA sequence evolution applicable to coding regions is
presented. This represents the first evolutionary model that accounts for
dependencies among nucleotides within a codon. The model uses the codon, as
opposed to the nucleotide, as the unit of evolution, and is parameterized
in terms of synonymous and nonsynonymous nucleotide substitution rates. One
of the model's advantages over those used in methods for estimating
synonymous and nonsynonymous substitution rates is that it completely
corrects for multiple hits at a codon, rather than taking a parsimony
approach and considering only pathways of minimum change between homologous
codons. Likelihood-ratio versions of the relative-rate test are constructed
and applied to data from the complete chloroplast DNA sequences of Oryza
sativa, Nicotiana tabacum, and Marchantia polymorpha. Results of these
tests confirm previous findings that substitution rates in the chloroplast
genome are subject to both lineage-specific and locus-specific effects.
Additionally, the new tests suggest tha the rate heterogeneity is due
primarily to differences in nonsynonymous substitution rates. Simulations
help confirm previous suggestions that silent sites are saturated, leaving
no evidence of heterogeneity in synonymous substitution rates.
相似文献
137.
ALEKSANDRA I. JOHANSEN ALICE EXNEROVÁ KATEŘINA HOTOVÁ SVÁDOVÁ PAVEL ŠTYS GABRIELLA GAMBERALE‐STILLE BIRGITTA S. TULLBERG 《Ecological Entomology》2010,35(5):602-610
1. Protective coloration in insects may be aposematic or cryptic, and some species change defensive strategy between instars. In Sweden, the adult striated shieldbugs Graphosoma lineatum (Heteroptera: Pentatomidae) undergo a seasonal colour change from pale brown and black striation in the pre‐hibernating adults, to red and black striation in the same post‐hibernating individuals. To the human eye the pre‐hibernating adults appear cryptic against the withered late summer vegetation, whereas the red and black post‐hibernating adults appear aposematic. This suggests a possibility of a functional colour change. However, what is cryptic to the human eye is not necessarily cryptic to a potential predator. 2. Therefore we tested the effect of coloration in adult G. lineatum on their detectability for avian predators. Great tits (Parus major) were trained to eat sunflower seeds hidden inside the emptied exoskeletons of pale or red G. lineatum. Then the detection time for both colour forms was measured in a dry vegetation environment. 3. The birds required a longer time to find the pale form of G. lineatum than the red one. The pale form appears more cryptic on withered late summer vegetation than the red form, not only to the human eye but also to avian predators. The result supports the idea that the adult individuals of G. lineatum undergo a functional change from a cryptic protective coloration to an aposematic one. 相似文献
138.
139.
Sawant SV Kiran K Mehrotra R Chaturvedi CP Ansari SA Singh P Lodhi N Tuli R 《Journal of experimental botany》2005,56(419):2345-2353
140.
Cryopreservation of flounder (Paralichthys olivaceus) sperm with a practical methodology 总被引:6,自引:0,他引:6
A simple and convenient protocol for the cryopreservation of the flounder (Paralichthys olivaceus) sperm was established for "on the spot" cryopreservation of large quantities of semen. The use of three cryoprotectants, dimethyl sulphoxide (DMSO), glycerol (Gly) and methanol was tested in the method. The percentage of motile sperm present in semen after it had been frozen and thawed in the presence of DMSO, Gly or methanol was 60.5+/-3.6, 79.17+/-4.5 and 13.25+/-4.7%, respectively. The fertilization rates of this sperm were 67.06+/-15.1, 76.20+/-10.0 and 44.93+/-22.6%, while the hatching rates of eggs fertilized with this sperm were 37.40+/-8.3, 48.18+/-25.7 and 23.35+/-10.8%, respectively. It was found that Gly and DMSO were better cryoprotectants than methanol, with Gly giving the best overall results. Under scanning electron microscopy, it could be seen that while the majority of the frozen-thawed sperm remained morphologically normal, some exhibited lost or dilated mitochondria, swollen mid-pieces, broken tails, or damaged cell membrane, which probably caused the decrease in motility and fertility of the frozen-thawed sperm. 相似文献