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排序方式: 共有184条查询结果,搜索用时 78 毫秒
31.
Erin S. Luetkemeier Ripan S. Malhi Jonathan E. Beever Lawrence B. Schook 《Immunogenetics》2009,61(2):119-129
The major histocompatibility complex (MHC) is an immunological gene-dense region of high diversity in mammalian species. Sus scrofa was domesticated by at least six independent events over Eurasia during the Holocene period. It has been hypothesized that
the level and distribution of MHC variation in pig populations reflect genetic selection and environmental influences. In
an effort to define the complexity of MHC polymorphisms and the role of selection in the generation of class II gene diversity
(DQB, DRB1, and pseudogene ΨDRB3), DNA from globally distributed unrelated domestic pigs of European and Asian origins and
a Suidae out-group was analyzed. The number of pseudogene alleles identified (ΨDRB3 33) was greater than those found in the
expressed genes (DQB 20 and DRB1 23) but the level of observed heterozygosity (ΨDRB3 0.452, DQB 0.732, and DRB1 0.767) and
sequence diversity (ΨDRB3 0.029, DQB 0.062, and DRB1 0.074) were significantly lower in the pseudogene, respectively. The
substitution ratios reflected an excess of d
N (DQB 1.476, DRB1 1.724, and ΨDRB3 0.508) and the persistence of expressed gene alleles suggesting the influence of balancing
selection, while the pseudogene was undergoing purifying selection. The lack of a clear MHC phylogeographic tree, coupled
with close genetic distances observed between the European and Asian populations (DQB 0.047 and DRB1 0.063) suggested that
unlike observations using mtDNA, the MHC diversity lacks phylogeographic structure and appears to be globally uniform. Taken
together, these results suggest that, despite regional differences in selective breeding and environments, no skewing of MHC
diversity has occurred.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
32.
Kitty F Verzijlbergen Alex W Faber Iris JE Stulemeijer Fred van Leeuwen 《BMC molecular biology》2009,10(1):76
Background
Methylation of lysine 79 on histone H3 by Dot1 is required for maintenance of heterochromatin structure in yeast and humans. However, this histone modification occurs predominantly in euchromatin. Thus, Dot1 affects silencing by indirect mechanisms and does not act by the recruitment model commonly proposed for histone modifications. To better understand the role of H3K79 methylation gene silencing, we investigated the silencing function of Dot1 by genetic suppressor and enhancer analysis and examined the relationship between Dot1 and other global euchromatic histone modifiers. 相似文献33.
Evolutionary dynamics of the kinetochore network in eukaryotes as revealed by comparative genomics 下载免费PDF全文
Jolien JE van Hooff Eelco Tromer Leny M van Wijk Berend Snel Geert JPL Kops 《EMBO reports》2017,18(9):1559-1571
During eukaryotic cell division, the sister chromatids of duplicated chromosomes are pulled apart by microtubules, which connect via kinetochores. The kinetochore is a multiprotein structure that links centromeres to microtubules, and that emits molecular signals in order to safeguard the equal distribution of duplicated chromosomes over daughter cells. Although microtubule‐mediated chromosome segregation is evolutionary conserved, kinetochore compositions seem to have diverged. To systematically inventory kinetochore diversity and to reconstruct its evolution, we determined orthologs of 70 kinetochore proteins in 90 phylogenetically diverse eukaryotes. The resulting ortholog sets imply that the last eukaryotic common ancestor (LECA) possessed a complex kinetochore and highlight that current‐day kinetochores differ substantially. These kinetochores diverged through gene loss, duplication, and, less frequently, invention and displacement. Various kinetochore components co‐evolved with one another, albeit in different manners. These co‐evolutionary patterns improve our understanding of kinetochore function and evolution, which we illustrated with the RZZ complex, TRIP13, the MCC, and some nuclear pore proteins. The extensive diversity of kinetochore compositions in eukaryotes poses numerous questions regarding evolutionary flexibility of essential cellular functions. 相似文献
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Adaptive population divergence and directional gene flow across steep elevational gradients in a climate‐sensitive mammal 下载免费PDF全文
Matthew D. Waterhouse Liesl P. Erb Erik A. Beever Michael A. Russello 《Molecular ecology》2018,27(11):2512-2528
The ecological effects of climate change have been shown in most major taxonomic groups; however, the evolutionary consequences are less well‐documented. Adaptation to new climatic conditions offers a potential long‐term mechanism for species to maintain viability in rapidly changing environments, but mammalian examples remain scarce. The American pika (Ochotona princeps) has been impacted by recent climate‐associated extirpations and range‐wide reductions in population sizes, establishing it as a sentinel mammalian species for climate change. To investigate evidence for local adaptation and reconstruct patterns of genomic diversity and gene flow across rapidly changing environments, we used a space‐for‐time design and restriction site‐associated DNA sequencing to genotype American pikas along two steep elevational gradients at 30,966 SNPs and employed independent outlier detection methods that scanned for genotype‐environment associations. We identified 338 outlier SNPs detected by two separate analyses and/or replicated in both transects, several of which were annotated to genes involved in metabolic function and oxygen transport. Additionally, we found evidence of directional gene flow primarily downslope from high‐elevation populations, along with reduced gene flow at outlier loci. If this trend continues, elevational range contractions in American pikas will likely be from local extirpation rather than upward movement of low‐elevation individuals; this, in turn, could limit the potential for adaptation within this landscape. These findings are of particular relevance for future conservation and management of American pikas and other elevationally restricted, thermally sensitive species. 相似文献
36.
37.
A large-subunit mitochondrial ribosomal DNA sequence translocated to the nuclear genome of two stone crabs (Menippe) 总被引:1,自引:0,他引:1
Two DNA sequences that appear to be homologous to large-subunit
mitochondrial ribosomal RNA genes have been identified in the stone crabs
Menippe mercenaria and M. adina. Amplification from whole genomic DNA by
polymerase chain reaction (PCR) with oligonucleotide primers based on
conserved portions of large-subunit mitochondrial rRNA genes consistently
amplified two products of similar length (565 and 567 bp). These products
differed at 3% of their nucleotide bases, and could be distinguished by a
HindIII site. Only one of these sequences (designated the A sequence) was
detected by PCR in purified mitochondrial DNA. The other (designated the B
sequence) hybridized to total genomic DNA at a level consistent with a
nuclear genome location. It is unlikely that the type B product would have
been recognized as a nuclear copy by examination of its sequence alone.
This is the first report of a mitochondrial gene sequence translocated into
the nuclear genome of a crustacean.
相似文献
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40.
Jonathan Beever 《Biosemiotics》2012,5(2):181-191
If the central problem in philosophical ethics is determining and defining the scope of moral value, our normative ethical theories must be able to explain on what basis and to what extent entities have value. The scientific foundation of contemporary biosemiotic theory grounds a theory of moral value capable of addressing this problem. Namely, it suggests that what is morally relevant is semiosis. Within this framework, semiosis is a morally relevant and natural property of all living things thereby offering us an ecological, as opposed to merely environmental, ethic. A consequence of this semiotic theory is that living things are accorded inherent moral value based on their natural relational properties—their ability to signify. This consequence establishes a hierarchy of inherent moral value based on the scope of signification: the larger the Umwelten, the greater the value. This paper argues that a robust semiotic moral theory can take into account a much wider scope of inherent value.. These consequences have positive ramifications for environmental ethics in their recognition of the natural ecological networks in which each organism is bound. This presentation of a biosemiotic model of value offers a justificatory strategy for our contemporary moral intuitions concerning our semiotic/moral relationships with living things while also productively pushing our normative ethical boundaries. 相似文献