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101.
102.
The unmasking of antigens in paraffin sections of tissue by trypsin. 总被引:21,自引:0,他引:21
103.
Petrified wood specimens from the Dakota Formation of Utah are here described as Agathoxylon lemonii . This new species is characterized by having distinct growth rings, araucarian tracheary pitting, resin plates or plugs in its tracheids, abundant axial parenchyma, low uniseriate rays and 1–4 small, slightly bordered pits with circular to oval included apertures per crossfield. This is the first report of petrified wood from the Dakota Formation of the western United States and the first record of Agathoxylon from North America. 相似文献
104.
Descurainia torulosa was established in 1983 based on material collected in northwestern Wyoming. The species is now known from 2 disjunct populations in southwestern Wyoming, and recent collections have expanded the known distribution within the northern portion of its range. The north-south disjunct distribution and apparent habitat differences have stimulated questions concerning the degree of relatedness between the disjunct elements to the point that the southern populations have been suggested to be a distinct taxon. Recognition of D. torulosa as a distinct species has also been questioned. This paper is based on field examination of D. torulosa populations, study of all known D. torulosa herbarium specimens, and analysis of nucleotide sequence from the internal transcribed spacer regions 1 and 2 of nuclear ribosomal DNA (ITS-1 & 2) from population exemplars. Cladistic analysis of the sequence data support our conclusion, based on morphological analysis. Northern and southern populations of D. torulosa are conspecific. Western North American Descurainia is in need of modern, critical taxonomic revision. 相似文献
105.
O?nopsis foliosa var. foliosa and var. monocephala are endemic to short-grass steppe of southeastern Colorado and until recently were considered geographically disjunct. The only known qualitative feature separating these 2 varieties is floral head type; var. foliosa has radiate heads, whereas var. monocephala heads are discoid. Sympatry between these varieties is restricted to a small area in which a range of parental types and intermediate head morphologies is observed. We used distribution mapping, morphometric analyses, chromosome cytology, and pollen stainability to characterize the sympatric zone. Morphometrics confirms that the only discrete difference between var. foliosa and var. monocephala is radiate versus discoid heads, respectively. The outer florets of putative hybrid individuals ranged from conspicuously elongated yet radially symmetric disc-floret corollas, to elongated radially asymmetric bilabiate- or deeply cleft corollas, to stunted ray florets with appendages remnant of corolla lobes. Chromosome cytology of pollen mother cells from both putative parental varieties and a series of intermediate morphological types collected at the sympatric zone reveal evidence of translocation heterozygosity. Pollen stainability shows no significant differences in viability between the parental varieties and putative hybrids. The restricted distribution of putative hybrids to a narrow zone of sympatry between the parental types and the presence of meiotic chromosome-pairing anomalies in these intermediate plants are consistent with a hybrid origin. The high stainability of putative-hybrid pollen adds to a growing body of evidence that hybrids are not universally unfit. 相似文献
106.
While a variety of mammalian megafauna have been recovered from sediments associated with Lake Bonneville, Utah, sloths have been notably rare. Three species of ground sloth, Megalonyx jeffersonii, Paramylodon harlani, and Nothrotheriops shastensis , are known from the western United States during the Pleistocene. Yet all 3 are rare in the Great Basin, and the few existing records are from localities on the basin margin. The recent discovery of a partial skeleton of Megalonyx jeffersonii at Point-of-the-Mountain, Salt Lake County, Utah, fits this pattern and adds to our understanding of the distribution and ecology of this extinct species. Its occurrence in Lake Bonneville shoreline deposits permits a reasonable age determination of between 22 and 13 ka. 相似文献
107.
Pryor WR Rymer AM Mitchell DG Hill TW Young DT Saur J Jones GH Jacobsen S Cowley SW Mauk BH Coates AJ Gustin J Grodent D Gérard JC Lamy L Nichols JD Krimigis SM Esposito LW Dougherty MK Jouchoux AJ Stewart AI McClintock WE Holsclaw GM Ajello JM Colwell JE Hendrix AR Crary FJ Clarke JT Zhou X 《Nature》2011,472(7343):331-333
Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity. 相似文献
108.
Chapman MA Lawrence MS Keats JJ Cibulskis K Sougnez C Schinzel AC Harview CL Brunet JP Ahmann GJ Adli M Anderson KC Ardlie KG Auclair D Baker A Bergsagel PL Bernstein BE Drier Y Fonseca R Gabriel SB Hofmeister CC Jagannath S Jakubowiak AJ Krishnan A Levy J Liefeld T Lonial S Mahan S Mfuko B Monti S Perkins LM Onofrio R Pugh TJ Rajkumar SV Ramos AH Siegel DS Sivachenko A Stewart AK Trudel S Vij R Voet D Winckler W Zimmerman T Carpten J Trent J Hahn WC Garraway LA Meyerson M Lander ES Getz G 《Nature》2011,471(7339):467-472
Multiple myeloma is an incurable malignancy of plasma cells, and its pathogenesis is poorly understood. Here we report the massively parallel sequencing of 38 tumour genomes and their comparison to matched normal DNAs. Several new and unexpected oncogenic mechanisms were suggested by the pattern of somatic mutation across the data set. These include the mutation of genes involved in protein translation (seen in nearly half of the patients), genes involved in histone methylation, and genes involved in blood coagulation. In addition, a broader than anticipated role of NF-κB signalling was indicated by mutations in 11 members of the NF-κB pathway. Of potential immediate clinical relevance, activating mutations of the kinase BRAF were observed in 4% of patients, suggesting the evaluation of BRAF inhibitors in multiple myeloma clinical trials. These results indicate that cancer genome sequencing of large collections of samples will yield new insights into cancer not anticipated by existing knowledge. 相似文献
109.
110.
Lorenzen ED Nogués-Bravo D Orlando L Weinstock J Binladen J Marske KA Ugan A Borregaard MK Gilbert MT Nielsen R Ho SY Goebel T Graf KE Byers D Stenderup JT Rasmussen M Campos PF Leonard JA Koepfli KP Froese D Zazula G Stafford TW Aaris-Sørensen K Batra P Haywood AM Singarayer JS Valdes PJ Boeskorov G Burns JA Davydov SP Haile J Jenkins DL Kosintsev P Kuznetsova T Lai X Martin LD McDonald HG Mol D Meldgaard M Munch K Stephan E Sablin M Sommer RS Sipko T Scott E Suchard MA Tikhonov A Willerslev R 《Nature》2011,479(7373):359-364
Despite decades of research, the roles of climate and humans in driving the dramatic extinctions of large-bodied mammals during the Late Quaternary period remain contentious. Here we use ancient DNA, species distribution models and the human fossil record to elucidate how climate and humans shaped the demographic history of woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox. We show that climate has been a major driver of population change over the past 50,000 years. However, each species responds differently to the effects of climatic shifts, habitat redistribution and human encroachment. Although climate change alone can explain the extinction of some species, such as Eurasian musk ox and woolly rhinoceros, a combination of climatic and anthropogenic effects appears to be responsible for the extinction of others, including Eurasian steppe bison and wild horse. We find no genetic signature or any distinctive range dynamics distinguishing extinct from surviving species, emphasizing the challenges associated with predicting future responses of extant mammals to climate and human-mediated habitat change. 相似文献