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61.
Yuri I. Wolf Eugene V. Koonin 《BioEssays : news and reviews in molecular, cellular and developmental biology》2013,35(9):829-837
A common belief is that evolution generally proceeds towards greater complexity at both the organismal and the genomic level, numerous examples of reductive evolution of parasites and symbionts notwithstanding. However, recent evolutionary reconstructions challenge this notion. Two notable examples are the reconstruction of the complex archaeal ancestor and the intron‐rich ancestor of eukaryotes. In both cases, evolution in most of the lineages was apparently dominated by extensive loss of genes and introns, respectively. These and many other cases of reductive evolution are consistent with a general model composed of two distinct evolutionary phases: the short, explosive, innovation phase that leads to an abrupt increase in genome complexity, followed by a much longer reductive phase, which encompasses either a neutral ratchet of genetic material loss or adaptive genome streamlining. Quantitatively, the evolution of genomes appears to be dominated by reduction and simplification, punctuated by episodes of complexification. 相似文献
62.
Virginia L. Naples 《Historical Biology》2013,25(2):187-206
Cranial musculature, dental function and mandibular movement patterns in Eremotherium laurillardi were reconstructed from the examination of crania and dentitions. Size, shape and pattern of muscle divisions were reconstructed from the examination of bony rugosities indicating muscle attachments. Details of masticatory muscle structure and function were based on dissections of the tree sloths Bradypus and Choloepus. Among sloths, masticatory muscles in E. laurillardi demonstrate a different synergist–antagonist pattern, reflecting greater emphasis on mediolateral mandibular movements. Eight cranial character complexes (anterior facial, zygomatic arch, superficial masseter, deep masseter–zygomaticomandibularis, pterygoid, temporal, occipital and occlusal) determined by interrelated contributions of each component made to group functions were identified. An elongate anterior face and predental spout in E. laurillardi allowed protrusion of a long narrow tongue at small degrees of gape, reflecting a probably ancestral xenarthran condition. Gape minimisation, in conjunction with the mediolaterally directed masticatory stroke in E. laurillardi, was a unique solution to increase masticatory efficiency by permitting molariform tooth shearing surfaces to remain in or near occlusion for a greater percentage of each chewing cycle. 相似文献
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Feng-Jung Chen Kuan-Wei Lee Chun-Chieh Lai Sue-Ping Lee Hsiao-Hsuian Shen Shu-Ping Tsai Bang-Hung Liu Ling-Mei Wang Gunn-Guang Liou 《Biochemical and biophysical research communications》2013
Receptor tyrosine kinases (RTKs) regulate many cellular processes, and Sprouty2 (Spry2) is known as an important regulator of RTK signaling pathways. Therefore, it is worth investigating the properties of Spry2 in more detail. In this study, we found that Spry2 is able to self-assemble into oligomers with a high-affinity KD value of approximately 16 nM, as determined through BIAcore surface plasmon resonance analysis. The three-dimensional (3D) structure of Spry2 was resolved using an electron microscopy (EM) single-particle reconstruction approach, which revealed that Spry2 is donut-shaped with two lip-cover domains. Furthermore, the method of energy dispersive spectrum obtained through EM was analyzed to determine the elements carried by Spry2, and the results demonstrated that Spry2 is a silicon- and iron-containing protein. The silicon may contribute to the electroconductivity of Spry2, and this property exhibits a concentration-dependent feature. This study provides the first report of a silicon- and iron-containing protein, and its 3D structure may allow us (1) to study the potential mechanism through the signal transduction is controlled by switching the electronic transfer on or off and (2) to develop a new type of conductor or even semiconductor using biological or half-biological hybrid materials in the future. 相似文献
66.
Estimates of population size are critical for conservation and management, but accurate estimates are difficult to obtain for many species. Noninvasive genetic methods are increasingly used to estimate population size, particularly in elusive species such as large carnivores, which are difficult to count by most other methods. In most such studies, genotypes are treated simply as unique individual identifiers. Here, we develop a new estimator of population size based on pedigree reconstruction. The estimator accounts for individuals that were directly sampled, individuals that were not sampled but whose genotype could be inferred by pedigree reconstruction, and individuals that were not detected by either of these methods. Monte Carlo simulations show that the population estimate is unbiased and precise if sampling is of sufficient intensity and duration. Simulations also identified sampling conditions that can cause the method to overestimate or underestimate true population size; we present and discuss methods to correct these potential biases. The method detected 2–21% more individuals than were directly sampled across a broad range of simulated sampling schemes. Genotypes are more than unique identifiers, and the information about relationships in a set of genotypes can improve estimates of population size. 相似文献
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目的:对比管状胃代食管术与全胃代食管术治疗食管癌的安全性与有效性。方法:2005年1月到2015年2月选择我院收治的100例食管癌患者,根据随机数字表法分为治疗组与对照组各50例,所有患者都行食管癌切除术,同时对照组给予全胃代食管手术,治疗组给予管状胃代食管术,对两组患者围手术指标、并发症及生活质量状况进行观察比较。结果:所有患者完成手术,治疗组的手术时间、术中出血量、术后住院时间、术后胃肠减压时间及术后闭式引流时间都明显少于对照组(P0.05)。治疗组术后3个月反流性食管炎、胃排空障碍、胸胃综合征、吻合口狭窄、吻合口瘘等并发症发生情况明显少于对照组(P0.05),日常生活、一般状况、治疗相关症状、社会影响、情感活动评分都明显高于对照组(P0.05)。结论:相对于全胃代食管术,管状胃代食管术在治疗食管癌患者中的应用具有更好的安全性与有效性,值得进一步临床研究与推广。 相似文献
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Virtual reconstruction of the Early Pleistocene mandible ATD6‐96 from Gran Dolina‐TD6‐2 (Sierra De Atapuerca,Spain) 下载免费PDF全文
70.
Howard Winant 《Ethnic and racial studies》2016,39(13):2285-2292
ABSTRACTEmirbayer and Desmond’s THE RACIAL ORDER is a heroic but ultimately quixotic effort. The work relies upon an attempted synthesis of Deweyan pragmatism and Bourdieuian social capital theory. Emirbayer and Desmond deploy an uneasy combination of approaches, insisting upon ‘reflexivity’ in sociological study of race and racism (the pragmatism dimension), and crafting a dubious taxonomy of sociological ‘fields’ where racial conflict takes shape, and in which sociologists study race as well (the social capital dimension). A chapter on ‘racial reconstruction’ proposes to apply their understanding to concrete political struggles, in pursuit of an augmented ‘racial democracy’. While the book is tremendously erudite theoretically and provides a valuable literature review, it does not advance racial theory very much. The authors are distracted by Bourdieu’s scientism and obsession with classification. Although ‘racial order’ is revealed to be a chimera, there is still much to be learned here. 相似文献