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排序方式: 共有167条查询结果,搜索用时 7 毫秒
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LOVE DALÉN EVA FUGLEI PÁLL HERSTEINSSON CHRISTIAN M. O. KAPEL JAMES D. ROTH GUSTAF SAMELIUS MAGNUS TANNERFELDT ANDERS ANGERBJÖRN 《Biological journal of the Linnean Society. Linnean Society of London》2005,84(1):79-89
The circumpolar arctic fox Alopex lagopus thrives in cold climates and has a high migration rate involving long-distance movements. Thus, it differs from many temperate taxa that were subjected to cyclical restriction in glacial refugia during the Ice Ages. We investigated population history and genetic structure through mitochondrial control region variation in 191 arctic foxes from throughout the arctic. Several haplotypes had a Holarctic distribution and no phylogeographical structure was found. Furthermore, there was no difference in haplotype diversity between populations inhabiting previously glaciated and unglaciated regions. This suggests current gene flow among the studied populations, with the exception of those in Iceland, which is surrounded by year-round open water. Arctic foxes have often been separated into two ecotypes: 'lemming' and 'coastal'. An analysis of molecular variance suggested particularly high gene flow among populations of the 'lemming' ecotype. This could be explained by their higher migration rate and reduced fitness in migrants between ecotypes. A mismatch analysis indicated a sudden expansion in population size around 118 000 BP, which coincides with the last interglacial. We propose that glacial cycles affected the arctic fox in a way opposite to their effect on temperate species, with interglacials leading to short-term isolation in northern refugia. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 79–89. 相似文献
95.
Rizos H McKenzie HA Ayub AL Woodruff S Becker TM Scurr LL Stahl J Kefford RF 《The Journal of biological chemistry》2006,281(49):38080-38088
Alterations in the p14(ARF) tumor suppressor are frequent in many human cancers and are associated with susceptibility to melanoma, pancreatic cancer, and nervous system tumors. In addition to its p53-regulatory functions, p14(ARF) has been shown to influence ribosome biogenesis and to regulate the endoribonuclease B23, but there remains considerable controversy about its nucleolar role. We sought to clarify the activities of p14(ARF) by studying its interaction with ribosomes. We show that p14(ARF) and B23 interact within the nucleolar 60 S preribosomal particle and that this interaction does not require rRNA. In contrast to previous reports, we found that expression of p14(ARF) does not significantly alter ribosome biogenesis but inhibits polysome formation and protein translation in vivo. These results suggest a ribosome-dependent p14(ARF) pathway that regulates cell growth and thus complements p53-dependent p14(ARF) functions. 相似文献
96.
Rev. David Paul D.D. LL.D. 《Plant Ecology & Diversity》2013,6(3):301-302
Background: Estuaries are characterised by salinity gradients and regular flooding events. These environmental factors form stress gradients, along which species composition changes. Aims: Analyse and compare patterns of plant species diversity along the estuarine salinity and flooding gradients of the Elbe and Connecticut Rivers. Methods: Vegetation was sampled at three elevations (low, mid, high) in five sites of each marsh type (fresh, brackish, salt) in both estuaries. Patterns of species density (SD) and evenness (E) along the gradients were analysed and compared between the two estuaries with three-factor ANOVAs. Results: The regional species pool was 33% higher for the Connecticut than for the Elbe. SD of fresh marshes (19 ± 2.2) was more than twice in the Connecticut than in the Elbe. We found an overall increase in SD from low to high elevation and from salt to freshwater marshes in both estuaries. However, SD and E were strongly depressed at intermediate elevations in the Elbe fresh and brackish marshes. Conclusions: Although diversity patterns in the two estuaries show overall similarities, patterns of SD and E differ, when particular elevational zones and marsh types are compared. We hypothesise this to be due to evolutionary and historical influences on the regional species pools, shaping the impact of local biotic and abiotic processes. 相似文献
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Seegmiller A; Williams KR; Hammersmith RL; Doak TG; Witherspoon D; Messick T; Storjohann LL; Herrick G 《Molecular biology and evolution》1996,13(10):1351-1362
Internal eliminated sequences (IESs) often interrupt ciliate genes in the
silent germline nucleus but are exactly excised and eliminated from the
developing somatic nucleus from which genes are then expressed. Some long
IESs are transposons, supporting the hypothesis that short IESs are ancient
transposon relics. In light of that hypothesis and to explore the
evolutionary history of a collection of IESs, we have compared various
alleles of a particular locus (the 81 locus) of the ciliated protozoa
Oxytricha trifallax and O. fallax. Three short IESs that interrupt two
genes of the locus are found in alleles from both species, and thus must be
relatively ancient, consistent with the hypothesis that short IESs are
transposon relics. In contrast, TBE1 transposon interruptions of the locus
are allele-specific and probably the results of recent transpositions.
These IESs (and the TBE1s) are precisely excised from the DNA of the
developing somatic macronucleus. Each IES interrupts a highly conserved
sequence. A few nucleotides at the ends of each IES are also conserved,
suggesting that they interact critically with IES excision machinery.
However, most IES nucleotide positions have evolved at high rates, showing
little or no selective constraint for function. Nonetheless, the length of
each IES has been maintained (+/- 3 bp). While one IES is approximately 33
bp long, three other IESs have very similar sizes, approximately 70 bp
long. Two IESs are surrounded by direct repeats of the sequence TTCTT. No
other sequence similarities were found between any of the four IESs.
However, the ends of one IES do match the inverted terminal repeat
consensus sequence of the "TA" IESs of Paramecium. Three O. trifallax
alleles appear to have been recipients in recent conversion events that
could have been provoked by double-strand breaks associated with IES ends
subsequent to IES transposition. Our findings support the hypothesis that
short IESs evolved from ancient transposons that have lost most of their
sequences, except those necessary for precise excision during macronuclear
development.
相似文献
99.
Rhodri J. LL. Williams David Robertson A. J. S. Davies 《The Histochemical journal》1989,21(5):271-278
Summary The purpose of this study was to determine whether the plant lectin,Dolichos biflorus agglutinin (DBA), can be used to recognize capillary endothelial cells and their processes during angiogenesis. By means of a peroxidase conjugate of DBA, blood vessels were visualized in whole mounts and ultrathin sections of mouse omentum. A part of this mesentery normally comprises an avascular membrane that is approximately 30 µm in thickness. Changes in the vascular plexus bordering this membrane were induced by intraperitoneal injection of irradiated Landschutz cells. Vascular endothelial cells were precisely and intensely stained, and vasculogenic processes were reliably distinguished from those of other cells. This technique permitted observation of the structure and distribution of capillary sprouts, and their relationship to each other and to pre-existing blood vessels. It was discovered that filiform projections extend from sprout apices. These projections may fuse allowing adjacent sprouts to form a new capillary loop. 相似文献
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