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排序方式: 共有108条查询结果,搜索用时 546 毫秒
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Mice of the TO Swiss strain received diets containing different amounts of saturated or unsaturated fat throughout life. These diets produced characteristic changes in cardiac phospholipid fatty acid composition, but produced no significant differences in fatty acid composition of phospholipids from a crude membrane fraction of brain. When littermates of these animals were exposed to ethanol vapour in an inhalation chamber it was observed that mice which had received a diet high in saturated fat lost the righting reflex at an estimated concentration of ethanol in blood higher than that required for mice receiving a control diet, or a diet rich in polyunsaturated fat. Analysis of the brain membrane fraction from those animals which had received ethanol revealed that mice receiving the highly saturated fat diet now had a significantly greater proportion of saturated fatty acids in brain membrane phospholipids. These results are discussed in relation to the hypothesis that brain membrane lipid composition may influence the behavioural response to ethanol. 相似文献
83.
Sze SH; Roytberg MA; Gelfand MS; Mironov AA; Astakhova TV; Pevzner PA 《Bioinformatics (Oxford, England)》1998,14(1):14-19
MOTIVATION: Gene annotation is the final goal of gene prediction
algorithms. However, these algorithms frequently make mistakes and
therefore the use of gene predictions for sequence annotation is hardly
possible. As a result, biologists are forced to conduct time-consuming gene
identification experiments by designing appropriate PCR primers to test
cDNA libraries or applying RT-PCR, exon trapping/amplification, or other
techniques. This process frequently amounts to 'guessing' PCR primers on
top of unreliable gene predictions and frequently leads to wasting of
experimental efforts. RESULTS: The present paper proposes a simple and
reliable algorithm for experimental gene identification which bypasses the
unreliable gene prediction step. Studies of the performance of the
algorithm on a sample of human genes indicate that an experimental protocol
based on the algorithm's predictions achieves an accurate gene
identification with relatively few PCR primers. Predictions of PCR primers
may be used for exon amplification in preliminary mutation analysis during
an attempt to identify a gene responsible for a disease. We propose a
simple approach to find a short region from a genomic sequence that with
high probability overlaps with some exon of the gene. The algorithm is
enhanced to find one or more segments that are probably contained in the
translated region of the gene and can be used as PCR primers to select
appropriate clones in cDNA libraries by selective amplification. The
algorithm is further extended to locate a set of PCR primers that uniformly
cover all translated regions and can be used for RT-PCR and further
sequencing of (unknown) mRNA.
相似文献
84.
Zimmerman PA; Katholi CR; Wooten MC; Lang-Unnasch N; Unnasch TR 《Molecular biology and evolution》1994,11(3):384-392
Polymerase chain reaction (PCR) products were characterized for a repeated
sequence family (designated "O-150") of the human filarial parasite
Onchocerca volvulus. In phylogenetic inferences, the O-150 sequences
clustered into closely related groups, suggesting that concerted evolution
maintains sequence homology in this family. Using a novel mathematical
model based on a nested application of an analysis of variance, we
demonstrated that African rainforest and savannah strain parasite
populations are significantly different. In contrast, parasites collected
in the New World are indistinguishable from African savannah strains of O.
volvulus. This finding supports the hypothesis that onchocerciasis was
recently introduced into the New World, possibly as a result of the slave
trade.
相似文献
85.
Bacterial endosymbionts are common in insects and can have dramatic effects on their host's evolution. So far, the only heritable symbionts found in Drosophila have been Wolbachia and Spiroplasma . While the incidence and effects of Wolbachia have been studied extensively, the prevalence and significance of Spiroplasma infections in Drosophila are less clear. These small, gram-positive, helical bacteria infect a diverse array of plant and arthropod hosts, conferring a variety of fitness effects. Male-killing Spiroplasma are known from certain Drosophila species; however, in others, Spiroplasma appear not to affect sex ratio. Previous studies have identified different Spiroplasma haplotypes in Drosophila populations, although no extensive surveys have yet been reported. We used a multilocus sequence analysis to reconstruct a robust Spiroplasma endosymbiont phylogeny, assess genetic diversity, and look for evidence of recombination. Six loci were sequenced from over 65 Spiroplasma -infected individuals from nine different Drosophila species. Analysis of these sequences reveals at least five separate introductions of four phylogenetically distinct Spiroplasma haplotypes, indicating that more extensive sampling will likely reveal an even greater Spiroplasma endosymbiont diversity. Patterns of variation in Drosophila mitochondrial haplotypes in Spiroplasma -infected and uninfected flies imply imperfect vertical transmission in host populations and possible horizontal transmission. 相似文献
86.
Genomic signatures of ancient asexual lineages 总被引:9,自引:0,他引:9
BENJAMIN B. NORMARK OLIVIA P. JUDSON NANCY A. MORAN 《Biological journal of the Linnean Society. Linnean Society of London》2003,79(1):69-84
Ancient asexuals – organisms that have lived without sex for millions of years – offer unique opportunities for discriminating among the various theories of the maintenance of sex. The last few years have seen molecular studies of a number of putative ancient asexual lineages, including bdelloid rotifers, Darwinulid ostracods, and mycorrhizal fungi. To help make sense of the diverse findings of such studies, we present a review and classification of the predicted effects of loss of sex on the eukaryotic genome. These include: (1) direct effects on the genetic structure of individuals and populations; (2) direct effects on the mutation rate due to the loss of the sexual phase; (3) decay of genes specific to sex and recombination; (4) effects of the cessation of sexual selection; (5) dis-adaptation due to the reduced efficiency of selection; and (6) adaptations to asexuality. We discuss the utility of the various predictions for detecting ancient asexuality, for testing hypotheses of the reversibility of a transition to asexuality, and for discriminating between theories of sex. In addition, we review the current status of putative ancient asexuals. © 2003 The Linnean Society of London. Biological Journal of the Linnean Society 2003, 79 , 69–84. 相似文献
87.
Molecular data support a rapid radiation of aphids in the Cretaceous and multiple origins of host alternation 总被引:10,自引:0,他引:10
CAROL D. VON DOHLEN NANCY A. MORAN 《Biological journal of the Linnean Society. Linnean Society of London》2000,71(4):689-717
Many aphids display a remarkably complex life cycle of host alternation, in which cyclical parthenogenesis is combined with the obligate use of two unrelated host plants. We used mitochondrial ribosomal DNA (partial 12S and 16S) sequences to reconstruct the phylogeny of aphids, to determine how many origins of host alternation and correlated major host-plant shifts have occurred. Our results agreed with previous morphological studies in that species clustered with good support at the level of tribes. There was little well-supported phylogenetic structure at levels deeper than tribes, however, except for the monophyly of two subfamilies, Aphidinae and Lachninae. We argue that aphids experienced a rapid radiation at the tribal level, after host shifting from gymnosperms to angiosperms. A rapid radiation is consistent with aphid fossils, which record the presence of few subfamilies in the late Cretaceous, but most extant tribes by the early Tertiary. Plant fossils also record host plants of aphid tribes diversifying during this time. A hypothesized mechanism by which host alternation has evolved (fundatrix specialization), coupled with the rapid radiation, implies that this life cycle may have originated as often as in the ancestor of each tribe that displays it. We also consider, however, an alternative hypothesis of fewer origins. The basal radiation of Aphididae was dated from molecular sequences to have occurred at approximately 80–150 Mya. 相似文献
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