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171.
Biased mutations and microsatellite variation 总被引:10,自引:6,他引:4
Mutation bias is one of the forces that may constrain the variation at
microsatellite loci. Here, we study the dynamics of population statistics
and the genetic distance between two populations under multiple stepwise
mutations with linear bias and random drift. Expressions are derived for
these statistics as functions of time, as well as at mutation-drift
equilibrium. Applying these expressions to published data on humans and
chimpanzees, the regression coefficient of mutation bias on allele size was
estimated to be at least between - 0.0064 and -0.013. The assumption of
mutational bias produces larger estimates of divergence times than are
obtained in its absence; in particular, the time of split between African
and non-African human populations is estimated to be between 183,000 and
222,000 years, assuming one-step mutations and no selection. With multistep
mutations, the divergence time is estimated to be lower.
相似文献
172.
Taxonomy lies at the heart of species conservation, yet many large New Zealand orthopterans remain undescribed. Among New Zealand’s anostostomatid wētā, Hemiandrus (ground wētā) is the most speciose genus but also the most poorly characterised and thus most in need of taxonomic and ecological work. Here we redescribe H. maculifrons and describe two new species of ground wētā previously encompassed by the specific name Hemiandrus maculifrons: Hemiandrus luna sp. nov. and H. brucei sp. nov. We also describe a morphologically similar and related species, Hemiandrus nox sp. nov.
http://zoobank.org/urn:lsid:zoobank.org:pub:71EA0879-A2F9-46B2-A105-E97A9AB25061
http://zoobank.org/References/71EA0879-A2F9-46B2-A105-E97A9AB25061 相似文献
173.
174.
Benthic insects in Swedish lake-outlet streams: patterns in species richness and assemblage structure 总被引:3,自引:0,他引:3
1. We studied how species richness of three hierarchical insect species groups, namely all benthic, lotic and filtering taxa, were related to a number of environmental variables in a data set from fifteen Swedish lake outlets. 2. In partial least-squares analyses, we found that size-related factors (stream width, discharge) and velocity-related factors (current velocity, substratum particle size) were positively associated, and productivity-related factors (chlorophyll a, seston energy, conductivity) negatively associated, with the species richness of the three groups. 3. The weak and negative relationship of richness with productivity largely negated theoretical predictions, whereas the species-environment results corroborated earlier findings from running water systems. 4. The most important factors associated with the species composition of the lake outlets studied included pH, lake area, discharge, channel width and detritus. 5. Of the filter feeders, most species of blackflies (Diptera: Simuliidae) showed a negative relationship with pH. 6. A nested subset analysis demonstrated that species-poor sites did not have a subset of species found at more species-rich sites in any of the three hierarchical groups. 相似文献
175.
176.
The effect of 200, 1000, and 5000 rads of mixed gamma-neutron radiations on total blood reducing sugar and blood glucose levels in guinea pigs was investigated 2 and 24 hours, and 9, 22, and 60 days postirradiation. In addition, the effectiveness of insulin and tolbutamide in these animals was evaluated before and after irradiation. Glucose increased to a lesser degree and later than did the nonglucose fraction of the blood sugar. Insulin and tolbutamide were at least as effective in irradiated animals as in unirradiated ones except after 5000 rads, when tolbutamide was significantly less effective. These results suggest that: (1) insufficient insulin is released by the pancreas in response to elevated blood sugar levels following irradiation; (2) the pancreas does produce insulin at these times and is able to release it in response to tolbutamide; and (3) a decrease in insulin production occurs following supralethal doses of radiation. 相似文献
177.
Inducible alkyltransferase DNA repair proteins in the filamentous fungus Aspergillus nidulans. 总被引:1,自引:1,他引:0 下载免费PDF全文
We have investigated the response of the filamentous fungus Aspergillus nidulans to low, non-killing, doses of the alkylating agent MNNG (N-methyl-N'-nitro-N-nitrosoguanidine). Such treatment causes a substantial induction of DNA alkyltransferase activity, with the specific activity in treated cells increasing up to one hundred-fold. Fluorography reveals the two main inducible species as proteins of 18.5 kDa and 21 kDa, both of which have activity primarily against O6-methylguanine (O6-MeG) lesions. In addition, two other alkyltransferase proteins can also be detected. One, of MW 16 kDa, is expressed in non-treated cells, but is not induced to the same extent as the 18.5 and 21 kDa proteins. The other, a protein of 19.5 kDa, is highly inducible and can only be detected in treated cells. Unlike the other three proteins, it acts primarily against methyl-phosphotriester (Me-PT) lesions. This is the first instance in which an MePT alkyltransferase has been detected in a eukaryotic organism and, coupled with the high level of induction of the O6-MeG alkyltransferase enzymes, this indicates that a control system similar to the bacterial adaptive response may be present in filamentous fungi. 相似文献
178.
Peter Strike 《Molecular & general genetics : MGG》1977,157(1):99-107
Summary Toluene treated cells have been used to study the processes of DNA synthesis and DNA degradation in ultra-violet irradiated Escherichia coli K12. Synthesis and degradation are both shown to occur extensively if polynucleotide ligase is inhibited, and to occur to a much lesser extent if ligase activity is optimal. Extensive UV-induced DNA synthesis in toluene-treated cells requires ATP for the initial incision step, and DNA polymerase I. Extensive degradation also depends on the early ATP-dependent incision step, and the subsequent degradation shows a partial requirement for ATP. Curtailment of degradation by ligase requires DNA polymerase activity, but is not dependent upon DNA polymerase I. Apparently this process can be carried out with equal facility by either DNA polymerase II or polymerase III. These observations suggest that extensive DNA polymerase I-dependent repair synthesis and extensive DNA degradation are facets of two divergent pathways of excision repair, both of which depend upon the early uvrABC determined ATP-dependent incision step. 相似文献
179.
ÅSA NORDIN 《Physiologia plantarum》1977,39(4):305-310
Roots of wheat seedlings (Triticum aestivum L. cv. Weibulls Starke) were cooled (+1°C) for 24 h while the shoots were kept at 25°C. The treatment induced an increased water deficit in the leaves. Fresh weight, dry weight, and the uptake and distribution of potassium and calcium were measured before and after cooling. Growth, measured both as fresh weight and dry weight increase, was reduced during the cold treatment. Afterwards (at 20°C), growth recovered to nearly pre-stress rates. Analysis of the potassium fluxes in and out of the roots by 86Rb techniques showed that influx, and to a lesser extent efflux, were inhibited at low temperature. The result was a net potassium uptake rate of one-third that of unstressed plants. After the cooling period the potassium influx increased to the rate of control plants. The potassium efflux increased to one and one-half times the rate of unstressed wheat so that net uptake was negative. The increase in potassium efflux was explained by a higher permeability of the root cell membranes after cooling. The net uptake of calcium was reduced to one-third by root cooling. Contrary to potassium uptake, calcium uptake increased under post-stress conditions, partly due to a low efflux rate. During root cooling there was a redistribution of dry matter from the leaves down towards the lower part of the shoot. Afterwards the original distribution of dry matter was reestablished. The net flow of potassium and calcium followed a similar pattern as dry matter, suggesting a growth-regulated flow. 相似文献
180.
The detection of a low level 45,X cell line during routine cytogenetic analysis in an adult female can be difficult to interpret. In the absence of recent information regarding loss of the X chromosome and ageing, we undertook a prospective study. A total of 19,650 cells from 655 females aged from birth to 80 years were screened cytogenetically. The frequency of X chromosome loss ranged from 0.07% at age <16 years to 7.3% at >65 years of age and showed a highly significant quadratic relationship between X chromosome loss and ageing (P < or = 0.00001). We have produced a graphic representation that provides a minimum baseline age-related rate of X chromosome loss. This should assist diagnostic cytogenetics laboratories to determine the significance of 45,X cell lines detected in women of all ages. We also compared the frequency of 45,X cells in women referred with at least one spontaneous abortion with those referred for other reasons and found no significant difference. Thus, in our population, an excess of 45,X cells is not associated with pregnancy loss. 相似文献