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1.
2.
Detecting non-neutral heterogeneity across a region of DNA sequence in the ratio of polymorphism to divergence 总被引:11,自引:4,他引:7
Natural selection, in the form of balancing selection or selective sweeps,
can result in a decoupling of the amounts of molecular polymorphism and
divergence. Thus natural selection can cause some areas of DNA sequence to
have greater silent polymorphism, relative to divergence between species,
than other areas. It would be useful to have a statistical test for
heterogeneity in the polymorphism to divergence ratio across a region of
DNA sequence, one that could identify heterogeneity greater than that
expected from the neutral processes of mutation, drift, and recombination.
The only currently available test requires that a region be arbitrarily
divided into sections that are compared with each other, and the
subjectivity of this division could be problematic. Here a test is proposed
in which runs of polymorphic and fixed sites are counted, where a "run" is
a set of one or more sites of one type preceded and followed by the other
type. The number of runs is smaller than otherwise expected if
polymorphisms are clumped together. By simulating neutral evolution and
comparing the observed number of runs to the simulations, a statistical
test is possible which does not require any a priori decisions about
subdivision.
相似文献
3.
Structure, Expression and Phylogenetic Analysis of the Gene Encoding Actin I in Pneumocystis Carinii 总被引:6,自引:0,他引:6
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L. D. Fletcher J. M. McDowell R. R. Tidwell R. B. Meagher C. C. Dykstra 《Genetics》1994,137(3):743-750
Actin is a major component of the cytoskeleton and one of the most abundant proteins found in eukaryotic cells. Comparative sequence analysis shows that this essential gene has been highly conserved throughout eukaryotic evolution making it useful for phylogenetic analysis. Complete cDNA clones for the actin-encoding gene were isolated and characterized from Pneumocystis carinii purified from immunosuppressed rat lungs. The nucleotide sequence encodes a protein of 376 amino acids. The predicted actin protein of P. carinii shares a high degree of conservation to other known actins. Only one major actin gene was found in P. carinii. The P. carinii actin sequence was compared with 30 other actin sequences. Gene phylogenies constructed using both neighbor-joining and protein parsimony methods places the P. carinii actin sequence closest to the majority of the fungi. Since the phylogenetic relationship of P. carinii to fungi and protists has been questioned, these data on the actin gene phylogeny support the grouping of P. carinii with the fungi. 相似文献
4.
After becoming nearly extinct during the Permian, the ferns began a slow recovery during the Triassic as the climate of the
earth moderated. As a result, a considerable number and variety were present and widely distributed during the Jurassic and
Early Cretaceous. However, with the rapid expansion of the angiosperms during the Late Cretaceous, the ferns once again became
reduced in variety and greatly restricted in distribution. Some of the Mesozoic ferns are rather primitive and obviously are
closely related descendants of Paleozoic taxa. Such ferns are assigned mostly to the Marattiaceae, Guaireaceae, Osmundaceae,
and Gleicheniaceae. The majority of the Mesozoic ferns, however, are distinctive and appear to have originated during that
era. These fossil ferns generally fit into modern orders and families such as the Matoniaceae or the Dipteridaceae. In some
cases, it is difficult to clearly distinguish some of the Mesozoic ferns from living genera.
A portion was presented as an invited paper to the symposium: Evolution of pteridophytes and gymnosperms at the XV International
Botanical Congress, Yokohama, Japan (1993). 相似文献
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Thirteen species of petrified wood have been assigned previously to the genus Paraphyllanthoxylon which was established by Bailey (1924) as representative of the section Phyllanthoideae of the family Euphorbiaceae. Mädel (1962) considered the genus Paraphyllanthoxylon representative of only the Glochidion wood group of the section Phyllanthoideae. This necessitates the establishment of a new genus, Phyllanthoideoxylon, for fossil woods which have characteristics in common with several of the other wood groups in the section Phyllanthoideae. The thirteen previously identified species of Paraphyllanthoxylon are reviewed and compared with the characteristics of the genus. Eleven of these species are retained in Paraphyllanthoxylon Bailey (emend. Mädel), one (P. bangalamodense) is assigned to Phyllanthoideoxylon nov. gen. and one (P. keriense) is transferred to Bridelioxylon Ramanujam. 相似文献
9.
Janine JH Oosterhof G Jolanda Elving Ietse Stokroos Arie van nieuw Amerongen Henny C van der Mei Henk J Busscher 《Biofouling》2013,29(6):347-353
The integrity of biofilms on voice prostheses used to rehabilitate speech in laryngectomized patients causes unwanted increases in airflow resistance, impeding speech. Biofilm integrity is ensured by extracellular polymeric substances (EPS). This study aimed to determine whether synthetic salivary peptides or mucolytics, including N-acetylcysteine and ascorbic acid, influence the integrity of voice prosthetic biofilms. Biofilms were grown on voice prostheses in an artificial throat model and exposed to synthetic salivary peptides, mucolytics and two different antiseptics (chlorhexidine and Triclosan). Synthetic salivary peptides did not reduce the air flow resistance of voice prostheses after biofilm formation. Although both chlorhexidine and Triclosan reduced microbial numbers on the prostheses, only the Triclosan-containing positive control reduced the air flow resistance. Unlike ascorbic acid, the mucolytic N-acetylcysteine removed most EPS from the biofilms and induced a decrease in air flow resistance. 相似文献
10.
Christian Burri Patrick D. Yeramian James L. Allen Ada Merolle Kazadi Kyanza Serge Alain Mpanya Pascal Lutumba Victor Kande Betu Ku Mesu Constantin Miaka Mia Bilenge Jean-Pierre Fina Lubaki Alfred Mpoo Mpoto Mark Thompson Blaise Fungula Munungu Francisco Manuel Théophilo Josenando Sonja C. Bernhard Carol A. Olson Johannes Blum Richard R. Tidwell Gabriele Pohlig 《PLoS neglected tropical diseases》2016,10(2)