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1.
2.
Joshua Isaacson 《Evolution; international journal of organic evolution》2019,73(7):1492-1493
Species adapt to the selective pressures of novel environments. Here, Gleditsch and Sperry tested whether four nonnative frugivorous bird species on the Hawaiian island of O'ahu diverged morphologically from their ancestral populations. They found that all four species significantly diverged from populations in their native ranges, with a general trend of smaller body size and larger bills. These differences were likely due to a combination of adaptive and nonadaptive processes. 相似文献
3.
Two phosphatidylcholines containing hydroxylated fatty acids, 1-palmitoyl-2-[5-hydroxy-6,8,11,14-eicosatetraenoyl]-sn-glycero-3- phosphocholine (1-palm-2-5HETE PC) and 1-palmitoyl-2-[15(S)-hydroxy-5,8,11,13- eicosatetraenoyl]-sn-glycero-3-phosphocholine (1-palm-2-15HETE PC), and one phosphatidylcholine containing nonhydroxylated fatty acids, 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine (1-palm-2-arach PC) were synthesized. Permeation of small nonelectrolytes (glycerol, 1,2-propanediol, urea, methylurea, propionamide and dimethylformamide) was assessed in multilamellar liposomes containing these synthetic PCs plus egg yolk phosphatidycholine (EPC) in the presence and absence of cholesterol. In liposomes containing 23% cholesterol, 69.3% EPC and 7.7% of either 1-palm-2-5HETE PC or 1-palm-2-15HETE PC the permeability to small nonelectrolytes was 60 to 400% greater than in liposomes containing 23% cholesterol and 77% EPC. The HETE-containing PCs also increased permeability in liposomes without cholesterol but the effects were less striking. Addition of the synthetic PCs did not affect the energy of activation of permeation. 相似文献
4.
MAJOR CLADES OF THE ANGIOSPERMS 总被引:2,自引:0,他引:2
ROLF DAHLGREN KÅRE BREMER 《Cladistics : the international journal of the Willi Hennig Society》1985,1(4):349-368
Abstract— Our knowledge of fundamental angiosperm interrelationships is still very incomplete. The absence of a narrowly circumscribed gymnosperm outgroup, ideally the sister group, makes character evaluation, necessary for a cladistic analysis, difficult. According to current views the superorder Magnoliiflorae with a number of other groups, for example the monocotyledons, may represent a complex of families near the base of the angiosperms. Interrelationships of groups within the monocotyledons are much better understood than those between groups within the dicotyledons. A cladogram of monocotyledon orders based on earlier work by R. Dahlgren, H. T. Clifford, and F. N. Rasmussen is presented. A data matrix for a sample of the angiosperms with 61 characters for 49 taxa, mostly magnoliifloran and related families, is presented. The characters are polarized mainly according to the current view that the primitive angiosperm morphotype is a woody dicotyledon with strobiloid flowers. As an alternative the matrix is adjusted following W. C. Burger's conjecture that the primitive angiosperm was a herbaceous monocotyledon with trimerous flowers. Both matrices were run in a computerized parsimony analysis, resulting in numerous equally parsimonious solutions. This result is illustrative of the great homoplasy in the available character information, and also of how little actually is known about fundamental angiosperm interrelationships or phylogeny. 相似文献
5.
Assignment of orthologous relationships among mammalian alpha-globin genes by examining flanking regions reveals a rapid rate of evolution 总被引:1,自引:0,他引:1
In order to study the relationships among mammalian alpha-globin genes, we
have determined the sequence of the 3' flanking region of the human alpha 1
globin gene and have made pairwise comparisons between sequenced
alpha-globin genes. The flanking regions were examined in detail because
sequence matches in these regions could be interpreted with the least
complication from the gene duplications and conversions that have occurred
frequently in mammalian alpha-like globin gene clusters. We found good
matches between the flanking regions of human alpha 1 and rabbit alpha 1,
human psi alpha 1 and goat I alpha, human alpha 2 and goat II alpha, and
horse alpha 1 and goat II alpha. These matches were used to align the
alpha-globin genes in gene clusters from different mammals. This alignment
shows that genes at equivalent positions in the gene clusters of different
mammals can be functional or nonfunctional, depending on whether they
corrected against a functional alpha-globin gene in recent evolutionary
history. The number of alpha-globin genes (including pseudogenes) appears
to differ among species, although highly divergent pseudogenes may not have
been detected in all species examined. Although matching sequences could be
found in interspecies comparisons of the flanking regions of alpha- globin
genes, these matches are not as extensive as those found in the flanking
regions of mammalian beta-like globin genes. This observation suggests that
the noncoding sequences in the mammalian alpha-globin gene clusters are
evolving at a faster rate than those in the beta-like globin gene clusters.
The proposed faster rate of evolution fits with the poor conservation of
the genetic linkage map around alpha-globin gene clusters when compared to
that of the beta-like globin gene clusters. Analysis of the 3' flanking
regions of alpha-globin genes has revealed a conserved sequence
approximately 100-150 bp 3' to the polyadenylation site; this sequence may
be involved in the expression or regulation of alpha-globin genes.
相似文献
6.
INTRODUCTI0NThedifferentiati0nofcelIsalongthemonocyte-macr0phagepathwayandthesig-nalsinvo1vedinthesecel1sacquiringtheabilitytokilltum0rcellsarenotfllllyundersto0d.Wehavebeenstudingamoleculewhichappearst0beanimportantmemberofthecytokinenetworkinvo1vedintheregulati0nmonocyteactivation.ThiscytokinetermedP48wasisolatedfr0mthehllmannullcellleukemiacell1ineReh.IthasbeenpurifiedtohomogeneityandfOundtobedistinctfrominterferongamma,col0nystimulatingfactors(CSFs)andTNFalphaalldbeta[1,2].Func-ti… 相似文献
7.
Pili of Pasteurella multocida of porcine origin 总被引:1,自引:0,他引:1
Abstract Using electron microscopy, pili with at least two distinct morphologies were observed on strains of Pasteurella multocida isolated from pigs with atrophic rhinitis. Rigid pili were found on 60–80% of all cells observed. These pili had a strong tendency to lie flat along the side of the outer cell membrane of P. multocida and as a result frequently were difficult to see. After growth in vitro, piliated P. multocida cells produced few pili (approx. 3–5 per cell). Heavily piliated cells were occasionally observed. The second type of pili were curly and also were difficult to visualize. Cells from cultures containing piliated cells failed to attach to red blood cells and to immobilized mucus. 相似文献
8.
9.
Thermophilic methane production from cattle waste 总被引:6,自引:0,他引:6
Methane production from waste of cattle fed a finishing diet was investigated, using four 3-liter-working volume anaerobic digestors at 60 degrees C. At 55 degrees C a start-up culture, in which waste was the only source of bacteria, was generated within 8 days and readily adapted to 60 degrees C, where efficiency of methanogenesis was greater. Increasing the temperature from 60 to 65 degrees C tended to drastically lower efficiency. When feed concentrations of volatile solids (VS, organic matter) were increased in steps of 2% after holding for 1 months at a given concentration, the maximum concentrations for efficient fermentation were 8.2, 10.0, 11.6, and 11.6% for the retention times (RT) of 3, 6, 9, and 12 days, respectively. The VS destructions for these and lower feed concentrations were 31 to 37, 36 to 40, 47 to 49 and 51 to 53% for the 3-, 6-, 9-, and 12-day RT digestors, respectively, and the corresponding methane production rates were about 0.16, 0.18, 0.20, and 0.22 liters/day per g of VS in the feed. Gas contained 52 to 57% methane. At the above RT and feed concentrations, alkalinity rose to 5,000 to 7,700 mg of CaCo3 per liter (pH to 7.5 to 7.8), NH3 plus NH4+ to 64 to 90 mM, and total volatile acids to 850 to 2,050 mg/liter as acetate. The 3-day RT digestor was quite stable up to 8.2% feed VS and at this feed concentration produced methane at the very high rate of 4.5 liters/day per liter of digestor. Increasing the percentage of feed VS beyond those values indicated above resulted in greatly decreased organic matter destruction and methane production, variable decrease in pH, and increased alkalinity, ammonia, and total volatile acid concentrations, with propionate being the first to accumulate in large amounts. In a second experiment with another lot of waste, the results were similar. These studies indicate that loading rates can be much higher than those previously thought useful for maximizing methanogenesis from cattle waste. 相似文献
10.
Gangliosides were compared with glycoproteins as potential receptors for Sendai virus by incorporating measured amounts of the glycoconjugates into lecithin-cholesterol liposomes and measuring binding by a hemagglutination assay with sheep erythrocytes. HeLa cell gangliosides showed no binding activity toward the virus up to 15 micrograms of sialic acid per 5 mumol of lecithin-cholesterol, whereas HeLa cell glycoproteins incorporated into similar liposomes caused avid virus binding below 1 microgram of sialic acid. These sialoglycoproteins could be separated from the bulk of cell proteins by multiple chloroform-methanol extractions. Purified rat brain gangliosides at a level of 120 micrograms of sialic acid in liposomes did not bind virus, whereas chloroform-methanol-extracted rat brain proteins caused only marginal binding. Bovine brain gangliosides differed slightly from the rat brain mixture in showing weak binding properties. Our results thus indicate that glycoproteins, rather than gangliosides, are the natural receptors for Sendai virus and that tissues differ as to the quantity of such protein receptors. 相似文献