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1.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
2.
Ten strains representing a novel genus of marine thermophilic archaebacteria growing at between 70 and 103°C with an optimal growth temperature of 100°C and a doubling time of only 37 min were isolated from geothermally heated marine sediments at the beach of Porto di Levante, Vulcano, Italy. The organisms are spherical-shaped, 0.8 to 2.5 m in width and exhibit monopolar polytrichous flagellation. They are strictly anaerobic heterotrophs, growing on starch, maltose, peptone and complex organic substrates. Only CO2 and H2 could be detected as metabolic products, the latter being inhibitory to growth at high concentrations. Hydrogen inhibition can be prevented by the addition of So, whereupon H2S is formed in addition, most likely as the result of a detoxification reaction. The GC-content of the DNA of isolate Vc 1 is 38 mol%. The new genus is named Pyrococcus, the fireball. Type species and strain is Pyrococcus furiosus Vc 1 (DSM 3638). 相似文献
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Calamagrostis villosa stands occurring in areas deforested by air-pollution impact in the Moravian-Silesian Beskydy Mountains were characterized by a high dry mass of total underground biomass (3 300 g. m?2—the slope site, 2 850 g. m?2—the flat site). The percentage of living roots and rhizomes in total underground biomass was very high (about 70%). The total aboveground biomass was respectively, 321 g.m?2 (the slope site) and 726 g. m?2 (the flat site). In unstabilized habitats on steep slope, the higher plant biomass produced was allocated to a more developed root system. 相似文献
5.
Ants are powerful model systems for the study of cooperation and sociality. In this review, we discuss how recent advances in ant genomics have contributed to our understanding of the evolution and organization of insect societies at the molecular level. 相似文献
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Triple resonance HCN and HCNCH experiments used in studies of 13C/15N labeled oligonucleotides include extended evolution periods (typically up to 100 ms) to allow coherence transfer through a complex heteronuclear spin network. Unfortunately, most of the magnetization is lost during the evolution due to fast spin–spin relaxation dominated by one-bond 1H–13C dipolar interaction. As demonstrated recently, the sensitivity of the experiments can be dramatically improved by keeping the spin system in a state of proton–carbon multiple-quantum coherence, which is not affected by the strong dipolar coupling. However, the multiple-quantum coherence is very sensitive to homonuclear as well as long-range heteronuclear interactions. Unwanted magnetization transfer due to these interactions can reduce the sensitivity back to the level of a single-quantum experiment and, for some spin moieties, even eliminate the signal completely. In the present paper we show that a modified HCN scheme that refocuses the interfering coherences improves sensitivity routinely by a factor of 1.5 to 4 over a nonselective experiment. In addition, novel multiple-quantum 2D and 3D HCNCH experiments with substantially enhanced sensitivity are presented. 相似文献
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Fiala K. etHerrera R. (1988): Living and dead belowground biomass and its distribution in some savanna communities in Cuba.—Folia Geobot. Phytotax., Praha, 23: 225–237.— The paper sums up the first results obtained from the study of belowground biomass estimated in natural and anthropic savanna communities in different regions of Cuba at the end of the 1984 rainy season. The percentage of living roots in total root biomass of natural savannas was lower (34–50%) than that in the anthropic savanna stands (68–74%). The total belowground biomass in three savanna stands ranged from 1,073 to 1,257 g. m?2. In the natural savanna stands 433 to 517 g. m?2 of living belowground biomass was found, which was less than in the anthropic savanna stand (745 g. m?2). In all the savanna stands studied, more than 80% of both the total and living belowground biomass were found in the upper 0–0.2 m soil layer. The share of the living biomass in the belowground plant organs varied from 71 to 79%. 相似文献