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991.
In this review, we focus on the assembly of DNA/protein complexes that trigger transposition in eukaryotic members of the
IS630–Tc1–mariner (ITm) super-family, the Tc1- and mariner-like elements (TLEs and MLEs). Elements belonging to this super-family encode transposases with DNA binding domains of different
origins, and recent data indicate that the chimerization of functional domains has been an important evolutionary aspect in
the generation of new transposons within the ITm super-family. These data also reveal that the inverted terminal repeats (ITRs) at the ends of transposons contain three kinds
of motif within their sequences. The first two are well known and correspond to the cleavage site on the outer ITR extremities,
and the transposase DNA binding site. The organization of ITRs and of the transposase DNA binding domains implies that differing
pathways are used by MLEs and TLEs to regulate transposition initiation. These differences imply that the ways ITRs are recognized
also differ leading to the formation of differently organized synaptic complexes. The third kind of motif is the transposition
enhancers, which have been found in almost all the functional MLEs and TLEs analyzed to date. Finally, in vitro and in vivo
assays of various elements all suggest that the transposition initiation complex is not formed randomly, but involves a mechanism
of oriented transposon scanning.
Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .
An erratum to this article can be found at 相似文献
992.
Genetic diversity in spring bread wheat (T.␣aestivum L.) was studied in a total of 69 accessions. For this purpose, 52 microsatellite (SSR) markers were used and a total of 406
alleles were detected, of which 182 (44.8%) occurred at a frequency of <5% (rare alleles). The number of alleles per locus
ranged from 2 to 14 with an average of 7.81. The largest number of alleles per locus occurred in the B genome (8.65) as␣compared
to the A (8.43) and D (5.93) genomes, respectively. The polymorphism index content (PIC) value varied from 0.24 to 0.89 with
an average of 0.68. The highest PIC for all accessions was found in the B␣genome (0.71) as compared to the A (0.68) and D␣genomes
(0.63). Genetic distance-based method (standard UPGMA clustering) and a model-based method (structure analysis) were used for cluster analysis. The two methods led to analogical results. Analysis of molecular variance (AMOVA)
showed that 80.6% of the total variation could be explained by the variance within the geographical groups. In comparison
to the diversity detected for all accessions (H
e
= 0.68), genetic diversity among European spring bread wheats was H
e
= 0.65. A comparatively higher diversity was observed between wheat varieties from Southern European countries (Austria/Switzerland,
Portugal/Spain) corresponding to those from other regions. 相似文献
993.
Evolutionary patterns in the antR-Cor gene in the dwarf dogwood complex (Cornus, Cornaceae) 总被引:1,自引:0,他引:1
The evolutionary pattern of the myc-like anthocyanin regulatory gene antR-Cor was examined in the dwarf dogwood species complex (Cornus Subgenus Arctocrania) that contains two diploid species (C. canadensis and C. suecica), their putative hybrids with intermediate phenotypes, and a tetraploid derivative (C. unalaschkensis). Full-length sequences of this gene (∼4 kb) were sequenced and characterized for 47 dwarf dogwood samples representing all
taxa categories from 43 sites in the Pacific Northwest. Analysis of nucleotide diversity indicated departures from neutral
evolution, due most likely to local population structure. Neighbor-joining and haplotype network analyses show that sequences
from the tetraploid and diploid intermediates are much more strongly diverged from C. suecica than from C. canadensis, and that the intermediate phenotypes may represent an ancestral group to C. canadensis rather than interspecific hybrids. Seven amino acid mutations that are potentially linked to myc-like anthocyanin regulatory
gene function correlate with petal colors differences that characterize the divergence between two diploid species and the
tetraploid species in this complex. The evidence provides a working hypothesis for testing the role of the gene in speciation
and its link to the petal coloration. Sequencing and analysis of additional nuclear genes will be necessary to resolve questions
about the evolution of the dwarf dogwood complex. 相似文献
994.
The detailed composition and structure of the Caenorhabditis elegans surface are unknown. Previous genetic studies used antibody or lectin binding to identify srf genes that play roles in surface determination. Infection by Microbacterium nematophilum identified bus (bacterially unswollen) genes that also affect surface characteristics. We report that biofilms produced by Yersinia pestis and Y. pseudotuberculosis, which bind the C. elegans surface predominantly on the head, can be used to identify additional surface-determining genes. A screen for C. elegans mutants with a biofilm absent on the head (Bah) phenotype identified three novel genes: bah-1, bah-2, and bah-3. The bah-1 and bah-2 mutants have slightly fragile cuticles but are neither Srf nor Bus, suggesting that they are specific for surface components involved in biofilm attachment. A bah-3 mutant has normal cuticle integrity, but shows a stage-specific Srf phenotype. The screen produced alleles of five known surface genes: srf-2, srf-3, bus-4, bus-12, and bus-17. For the X-linked bus-17, a paternal effect was observed in biofilm assays. 相似文献
995.
996.
Plant species may remain morphologically distinct despite gene exchange with congeners, yet little is known about the genomewide pattern of introgression among species. Here we analyze the effects of persistent gene flow on genomic differentiation between the sympatric sunflower species Helianthus annuus and H. petiolaris. While the species are strongly isolated in testcrosses, genetic distances at 108 microsatellite loci and 14 sequenced genes are highly variable and much lower (on average) than for more closely related but historically allopatric congeners. Our analyses failed to detect a positive association between levels of genetic differentiation and chromosomal rearrangements (as reported in a prior publication) or proximity to QTL for morphological differences or hybrid sterility. However, a significant increase in differentiation was observed for markers within 5 cM of chromosomal breakpoints. Together, these results suggest that islands of differentiation between these two species are small, except in areas of low recombination. Furthermore, only microsatellites associated with ESTs were identified as outlier loci in tests for selection, which might indicate that the ESTs themselves are the targets of selection rather than linked genes (or that coding regions are not randomly distributed). In general, these results indicate that even strong and genetically complex reproductive barriers cannot prevent widespread introgression. 相似文献
997.
Drosophila G9a is a nonessential gene 总被引:1,自引:1,他引:0
Mammalian G9a is a euchromatic histone H3 lysine 9 (H3K9) methyltransferase essential for development. Here, we characterize the Drosophila homolog of G9a, dG9a. We generated a dG9a deletion allele by homologous recombination. Analysis of this allele revealed that, in contrast to recent findings, dG9a is not required for fly viability. 相似文献
998.
Identification of selective sweeps using a dynamically adjusted number of linked microsatellites 下载免费PDF全文
There is currently large interest in distinguishing the signatures of genetic variation produced by demographic events from those produced by natural selection. We propose a simple multilocus statistical test to identify candidate sites of selective sweeps with high power. The test is based on the variability profile measured in an array of linked microsatellites. We also show that the analysis of flanking markers drastically reduces the number of false positives among the candidates that are identified in a genomewide survey of unlinked loci and find that this property is maintained in many population-bottleneck scenarios. However, for a certain range of intermediately severe population bottlenecks we find genomic signatures that are very similar to those produced by a selective sweep. While in these worst-case scenarios the power of the proposed test remains high, the false-positive rate reaches values close to 50%. Hence, selective sweeps may be hard to identify even if multiple linked loci are analyzed. Nevertheless, the integration of information from multiple linked loci always leads to a considerable reduction of the false-positive rate compared to a genome scan of unlinked loci. We discuss the application of this test to experimental data from Drosophila melanogaster. 相似文献
999.
Diversification and speciation processes are influenced by intrinsic (ecological specialization, dispersal) and extrinsic
(habitat structure and instability) factors, but the effect of ecological characteristics on dispersal is difficult to assess.
This study uses mitochondrial control region sequences to investigate the population structure and demographic history of
the endemic Lake Tanganyika cichlid Neolamprologus caudopunctatus with a preference for the rock-sand interface along two stretches of continuous, rocky shoreline, and across a sandy bay
representing a potential dispersal barrier. Populations along uninterrupted habitat were not differentiated; whereas, the
sandy bay separated two reciprocally monophyletic clades. The split between the two clades between 170,000 and 260,000 years
BP coincides with a period of rising water level following a major lowstand, and indicates that clades remained isolated throughout
subsequent lake level fluctuations. Low long-term effective population sizes were inferred from modest genetic diversity estimates,
and may be due to recent population expansions starting from small population sizes 45,000–60,000 years BP. Comparisons with
available data from specialized rock-dwelling species of the␣same area suggest that habitat structure and lake level fluctuations
determine phylogeographic patterns on large scales, while fine-scale population structure and demography are modulated by
species-specific ecologies. 相似文献
1000.
Genomewide association analysis in diverse inbred mice: power and population structure 总被引:4,自引:0,他引:4 下载免费PDF全文
McClurg P Janes J Wu C Delano DL Walker JR Batalov S Takahashi JS Shimomura K Kohsaka A Bass J Wiltshire T Su AI 《Genetics》2007,176(1):675-683
The discovery of quantitative trait loci (QTL) in model organisms has relied heavily on the ability to perform controlled breeding to generate genotypic and phenotypic diversity. Recently, we and others have demonstrated the use of an existing set of diverse inbred mice (referred to here as the mouse diversity panel, MDP) as a QTL mapping population. The use of the MDP population has many advantages relative to traditional F(2) mapping populations, including increased phenotypic diversity, a higher recombination frequency, and the ability to collect genotype and phenotype data in community databases. However, these methods are complicated by population structure inherent in the MDP and the lack of an analytical framework to assess statistical power. To address these issues, we measured gene expression levels in hypothalamus across the MDP. We then mapped these phenotypes as quantitative traits with our association algorithm, resulting in a large set of expression QTL (eQTL). We utilized these eQTL, and specifically cis-eQTL, to develop a novel nonparametric method for association analysis in structured populations like the MDP. These eQTL data confirmed that the MDP is a suitable mapping population for QTL discovery and that eQTL results can serve as a gold standard for relative measures of statistical power. 相似文献