Navegando por Palavras-chave "positive selection"
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- ItemSomente MetadadadosAdaptive algorithms applied to accelerometer biometrics in a data stream context(Ios Press, 2017) Pisani, Paulo Henrique; Lorena, Ana Carolina[UNIFESP]; de Carvalho, Andre C. P. L. F.The use of smartphone devices has increased over the last years, as illustrated by the growth in smartphone sales. These devices are currently used for several services, such as bank account access, social networks and storage of personal information. In view of this scenario, an important question arises: does authentication mechanisms already present in these devices provide enough security? Recently, a new authentication method, named accelerometer biometrics, has been proposed. This method allows the authentication of users using accelerometer data, which can be obtained from accelerometers usually present in modern smartphones. This is a clear advantage of this biometric modality, as there would be no additional cost with hardware. However, as a behavioral biometric technology, user models induced from accelerometer data may become outdated over time. This paper investigates the use of adaptation mechanisms to update user models in accelerometer biometrics in a data stream context. Practical issues regarding the usage of accelerometer data are also discussed.
- ItemSomente MetadadadosSelective pressures of human immunodeficiency virus type 1 (HIV-1) during pediatric infection(Elsevier B.V., 2007-12-01) Leal, Elcio [UNIFESP]; Janini, Mario [UNIFESP]; Diaz, Ricardo S. [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)Pediatric HIV-1 infection presents remarkable features that are distinct from those observed in adult infection. in vertically HIV-1-infected children, the viral load declines more slowly, and the cytotoxic T-lymphocyte response emerges late, only after the sixth month of life. This response generally tends to be narrow and less intense than that seen in adults. While the nuances of immune response at the cellular level during pediatric HIV-1 infection have been addressed, there is a lack of studies focusing on the consequences of this delayed and narrowed immune response at the population level. To better explore these features, we evaluated the selection regimen in gag, pol and env gene fragments of HIV-1 during pediatric infection. We estimated the number of nonsynonymous substitutions (d(N)) and synonymous substitutions (d(S)) codon-by-codon, using the maximum likelihood method and a modified counting method. Notably, both methods indicated a similar intensity of selection (measure by mean d(N)/d(S) ratio) between children and adults. Additionally, sites under positive selection were equally distributed along HIV genes and the location of these sites was analogous between children and adults. Therefore, the selective regimen in HIV during pediatric infection is equally broad and intense likewise the observed in adults. Unexpectedly, our phylogenetic-based analysis enabled us to identify two regions in the env gene of HIV with distinct adaptive functions. the first region, located in the vicinity of V3 loop, contains sites that might increase viral fitness within-host during antibody attack and virus-cell interaction. the second region, restricted to amino acids 334-368 of Gp160, contains sites that might increase viral fitness during interhost transmission at the population level. (C) 2007 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosSelective regimen shift and demographic growth increase associated with the emergence of high-fitness variants of canine parvovirus(Elsevier B.V., 2007-06-01) Pereira, Cesar A. D.; Leal, Elcio S.; Durigon, Edison Luiz; Universidade Federal de São Paulo (UNIFESP); Univ Anhembi Morumbi; Univ Santo Amaro; Universidade de São Paulo (USP)The natural evolution of Canine parvovirus (CPV) is characterized by a variety of mutations, mainly in the VP1/VP2 gene. Although positive selection has been previously reported in CPV, little is known about its overall contribution to viral adaptation in the canine population. Herein, the influences of the evolutive constraints on CPV during a period of viral adaptation into a previously uninfected population are more clearly investigated. To do this, 31 sequences of VP1/VP2 gene obtained from symptomatic domestic dogs in Brazil were used, sampled from 1980 to 2000. Marked evolutionary changes in CPV associated with a process of fine-tuning adaptation were observed. Specifically, sequences from the 1980s revealed two distinct antigenic types (i.e. 2a and 2b) cocirculating in Brazil. Moreover, analysis of the selective regimen showed that 90% of the VP2 sites were conserved (d(N/)d(s) = 0). in contrast, sequences from the 1990s were composed solely of CPV-2a with 96% of VP2 sites under purifying selection (d(N)/d(s) < 1) and site 297 under strong positive selection (omega = 4.9). Important features regarding the demographic history of CPV in Brazil were also observed. the viral population size passed through a short period of explosive growth that declined and then stabilized into a constant rate of spread. Remarkably, the explosive growth coincided with the appearance of CPV variants that presented a unique repertoire of mutations never before seen in other worldwide strains. the analysis also showed that the estimated nucleotide substitution was similar to those commonly observed in fast evolving RNA viruses. the present results demonstrated the adaptive potential of CPV to acquire, in short interval of 10 years, key mutations in the VP1/VP2 gene that increased viral fitness and enabled the virus to disseminate even in vaccinated dogs. (C) 2006 Elsevier B.V. All rights reserved.