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Comparisons of the molecular evolutionary process at rbcL and ndhF in the grass family (Poaceae) 总被引:2,自引:1,他引:1
We examine rate heterogeneity among evolutionary lineages of the grass
family at two plasmid loci, ndhF and rbcL, and we introduce a method to
determine whether patterns of rate heterogeneity are correlated between
loci. We show both that rates of synonymous evolution are heterogeneous
among grass lineages and that are heterogeneity is correlated between loci
at synonymous sites. At nonsynonymous sites, the pattern of rate
heterogeneity is not correlated between loci, primarily due to an aberrant
pattern of rate heterogeneity at nonsynonymous sites of rbcL. We compare
patterns of synonymous rate heterogeneity to predictors based on the
generation time effect and the speciation rate hypotheses. Although there
is some evidence for generation time effects, neither generation time
effects nor speciation rates appear to be sufficient to explain patterns of
rate heterogeneity in the grass plastid sequences.
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Dalu A Blaydes BS Bryant CW Latendresse JR Weis CC Barry Delclos K 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2002,777(1-2):249-260
Steroid hormones and their receptors play critical roles in the growth, development, and maintenance of the male reproductive tract. Genistein, a naturally occurring isoflavonoid primarily found in soybeans, interacts with estrogen receptors alpha and beta (ER alpha and beta), with preferential affinity for ER beta. This is one mechanism whereby genistein may affect growth and development and potentially alter susceptibility to carcinogenesis. Previous studies have indicated effects of soy and/or genistein in the male rodent reproductive tract under certain exposure conditions. The current study was undertaken to determine if modulation of the expression of ER alpha and ER beta by dietary genistein may contribute to those effects. Rats in a two-generation study were fed 0, 5, 100, or 500 ppm genistein prior to mating and through pregnancy and lactation. At weaning, male pups were selected in each of the F(1) and F(2) generations and half of the pups continued on the same diet as their dams (G/G, continuous exposure) while their litter mates were placed on control chow (G/C, gestational and lactational exposure) until sacrifice on PND 140. Male reproductive organ weights, serum levels of testosterone and dihydrotestosterone (DHT), and ER alpha and ER beta protein levels in the ventral and dorsolateral prostate were the endpoints measured. Prostate sections were also evaluated microscopically. Statistically significant elevations in testosterone and DHT were observed in PND 140 animals from the F(1) generation, but they were not accompanied by organ weight changes. Body weight in the continuously dosed 500 ppm F(1) PND 140 animals was depressed relative to control, but organ weights in animals of either generation showed few treatment-related effects. While estrogen receptor levels were quite variable, levels of ER beta in the dorsolateral prostate were significantly depressed in all dose groups in the G/C exposure and the high dose group of the G/G exposure in F(1) rats, but not in F(2) rats. Given the growing body of knowledge on the significance of ER beta in the prostate, the evidence for apparent down regulation of this receptor by genistein may have implications for reproductive toxicity and carcinogenesis that warrant further investigation. 相似文献
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The SNRPN gene is known to be expressed exclusively from the paternal allele and to map to the critical region for the neurobehavioral
disorder, Prader-Willi syndrome (PWS). As a means to investigate the mechanism of imprinting for the SNRPN gene, we have sought
to recapitulate the imprinted expression of the endogenous gene. Using an 85-kb murine Snrpn clone, containing 33 kb of 5′ and 30 kb of 3′ flanking DNA, we obtained two intact transgenic lines. One line, containing
two copies of the Snrpn transgene, recapitulated the imprinted expression pattern of the endogenous locus, whereas the other transgenic line, containing
a single copy, was expressed upon both maternal and paternal inheritance. This suggests that a 6.6-kb region of maternal-specific
DNA methylation that we have identified may be sufficient to confer imprinted expression, but not in a copy-number independent
manner. Finally, we produced five lines of transgenic mice using a 76-kb human SNRPN clone containing 45 kb and 7 kb of 5′
and 3′ flanking DNA, respectively. We found all the lines were expressed upon both maternal and paternal inheritance, regardless
of copy number, suggesting that the imprinting machinery in mouse and human may have diverged.
Received: 11 November 1998 / Accepted: 29 January 1999 相似文献
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Climate change poses an unprecedented threat to biodiversity worldwide. Consequently, unrecognised taxa may not receive adequate conservation attention to survive. We used molecular and morphological data to address the challenge of species delimitation within the genus Schilbe. The presence or absence of an adipose fin and distribution based on east-flowing, conceivably faster-flowing, or west-flowing, probably more slow-flowing, river systems were considered. Distinctive geographic patterns in genetic variation within southern, eastern, and western African populations were revealed. Particularly, the South African population is distinct from those of Namibia, Botswana and Nigeria. No individuals with rudimentary adipose fins were found at any locality, but specimens from three localities either had or did not have adipose fins. These mixed occurrences are suspected to be a result of human interventions, and that the presence of rudimentary adipose fins in the east African species could be an adaptive feature that serves to stabilise these fish in faster currents. In addition, the genetic divergence observed among African silver catfish from geographically isolated river systems is conceivably the result of micro-evolutionary adaptive responses to different environmental conditions. Collectively, these results distinguish S. depressirostris from S. intermedius. 相似文献
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We used simulated data to investigate a number of properties of maximum-
likelihood (ML) phylogenetic tree estimation for the case of four taxa.
Simulated data were generated under a broad range of conditions, including
wide variation in branch lengths, differences in the ratio of transition
and transversion substitutions, and the absence of presence of
gamma-distributed site-to-site rate variation. Data were analyzed in the ML
framework with two different substitution models, and we compared the
ability of the two models to reconstruct the correct topology. Although
both models were inconsistent for some branch-length combinations in the
presence of site-to-site variation, the models were efficient predictors of
topology under most simulation conditions. We also examined the performance
of the likelihood ratio (LR) test for significant positive interior branch
length. This test was found to be misleading under many simulation
conditions, rejecting too often under some simulation conditions. Under the
null hypothesis of zero length internal branch, LR statistics are assumed
to be asymptotically distributed chi 2(1); with limited data, the
distribution of LR statistics under the null hypothesis varies from chi
2(1).
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