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1.

Phylogenetic networks are a type of leaf-labelled, acyclic, directed graph used by biologists to represent the evolutionary history of species whose past includes reticulation events. A phylogenetic network is tree–child if each non-leaf vertex is the parent of a tree vertex or a leaf. Up to a certain equivalence, it has been recently shown that, under two different types of weightings, edge-weighted tree–child networks are determined by their collection of distances between each pair of taxa. However, the size of these collections can be exponential in the size of the taxa set. In this paper, we show that, if we have no “shortcuts”, that is, the networks are normal, the same results are obtained with only a quadratic number of inter-taxa distances by using the shortest distance between each pair of taxa. The proofs are constructive and give cubic-time algorithms in the size of the taxa sets for building such weighted networks.

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2.
We describe a riboprinting scheme for identification of unknown Acanthamoeba isolates at the species level. It involved the use of PCR-RFLP of small subunit ribosomal RNA gene (riboprint) of 24 reference strains by 4 kinds of restriction enzymes. Seven strains in morphological group I and III were identified at species level with their unique sizes of PCR product and riboprint type by Rsa I. Unique RFCP of 17 strains in group II by Dde I, Taq I and Hae III were classified into: (1) four taxa that were identifiable at the species level, (2) a subgroup of 4 taxa and a pair of 2 taxa that were identical with each other, and (3) a species complex of 7 taxa assigned to A. castellanii complex that were closely related. These results were consistent with those obtained by 18s rDNA sequence analysis. This approach provides an alternative to the rDNA sequencing for rapid identification of a new clinical isolate or a large number of environmental isolates of Acanthamoeba.  相似文献   

3.
The chromosome number 2n = 24 was determined in 31 taxa of Heliconia , representing nearly the entire morphological spectrum of the genus. The karyotype is a graded series of rather small chromosomes ranging between 0.7 and 1.7 urn. One pair has satellites. It is concluded that morphological chromosome differentiation played no great part in the diversification of the genus.  相似文献   

4.
Cope's Rule refers to the tendency of body size to increase along an evolutionary lineage. This rule is commonly tested by comparing size differences in pairs of taxa, one of which is assumed to be ancestral to the other. It has recently been pointed out that this approach fails to account for the unknown number of speciation events separating each pair. Here, a test that does account for this degree of separation is described and applied to some published data for dinosaurs. A by-product of the analysis is an estimate of the origination rate of dinosaur species.  相似文献   

5.
淫羊藿是我国特有且传统的重要药用植物,逐渐步入大宗品种行列。物种的准确鉴定是药效保障和用药安全的前提,为促进其资源的合理开发和利用,该文对淫羊藿属分类学研究进行系统梳理,并对其中存在的问题及存疑类群进行阐述。淫羊藿属共发表68种,中国58种(85.3%),其中57种为特有分布,具有显著的资源优势。淫羊藿属中国类群的分类学研究较为特殊,共26种集中发表于1990s,共31种(53.4%)为国外研究者命名,且绝大多数依据少量栽培个体命名。由于缺乏广泛的形态调查和性状变异分析,导致大量类群的形态描述不准确或不全面,后续20个类群被归并或降级。依据栽培个体命名的类群是补充描述和分类修订的重点。花色、根茎类型、花茎叶的数量及着生方式等性状在中国类群中存在广泛变异。经分类修订后,该属目前包括46种、1亚种和2变种。淫羊藿属中国组类群仍处于活跃进化中,其形态变异复杂,种间关系无法得到解决,为该属分类的最大挑战。但种质资源的研究和利用需要建立在清晰的分类学基础上。未来研究应基于居群调查,完善各物种的形态描述;在此基础上,整合形态变异特征、地理分布格局和基因序列特征,检测自然种间杂交事件,从而揭示物种的分化和进化历程。  相似文献   

6.
We have confirmed through an enlarged set of 728 species with 10,000 or more compiled codons, and a subset of 237 species with at least 50,000 compiled codons, that the mean values of a previously described index phi [the mean value of the ratio between the relative (G, C) content of Class II and Class I codons, where G and C are guanine and cytosine] decrease monotonically across five large taxa, viz archaea, bacteria, eukaryotes (excluding metazoa), metazoa (excluding vertebrates) and vertebrates. It is proposed that these main taxa diverge successively from an ancestral progenome along lines which have persisted over long periods of time, leading to a primordial non-symmetrical phylogenetic tree. Further divergence, i.e. from eukaryotes to plants, fungi and protozoans, has followed symmetrical branching with approximately equal numbers of replacements and fixations. A statistical analysis of the phi values of twelve distinct proteins, distributed over more than one thousand species belonging to the five main groups, was made to verify whether older taxa have older proteins. This supposition was confirmed for the first four taxa, but it was inconclusive for the last pair, metazoa/vertebrates.  相似文献   

7.
Univalent behaviour at anaphase I in desynaptic rye   总被引:1,自引:0,他引:1  
The Anaphase-I behaviour of univalents produced by desynapsis has been studied in four inbred lines of rye. — The analyses show that the distribution of numbers of equationally dividing univalents per cell at anaphase-I does not conform to the statistical expectation of randomness. The pattern of this distribution leads us to the assumption that two types of univalent pairs are present at metaphase I: in type I both members of the pair can divide equationally or reductionally, independent of one another. In type II both members of the pair always divide reductionally. Under this assumption a theoretical model was made which fits the observed distribution of the number of equationally dividing univalents per cell. — It is suggested that the difference of anaphase-I behaviour between these two types of univalent pairs is determined by the moment of metaphase I at which they are formed.  相似文献   

8.
A probabilistic method of paleobiogeographic analysis   总被引:1,自引:0,他引:1  
Existing methods of quantitative paleobiogeographic analysis, based on the statistical use of binary similarity coefficients, are shown to be defective. A new method employing a formal probability frequency function which relates the number of shared taxa to sample size and inferred population size for a pair of areas, is introduced. It assumes random selection of taxonomic samples by the fossil record from larger complete populations originally occurring in the areas concerned. Quantitative assessment of population diversity as well as population similarity expressed as percentage overlap with attendant error estimates result from the method, but the final phase of analysis remains, of necessity, both manual and inexact. Utility of the method is demonstrated by working simulated data and actual data pertaining to late Cretaceous ammonites.  相似文献   

9.
Understanding the evolution of mating systems, a central topic in evolutionary biology for more than 50 years, requires examining the genetic consequences of mating and the relationships between social systems and mating systems. Among pair-living mammals, where genetic monogamy is extremely rare, the extent of extra-group paternity rates has been associated with male participation in infant care, strength of the pair bond and length of the breeding season. This study evaluated the relationship between two of those factors and the genetic mating system of socially monogamous mammals, testing predictions that male care and strength of pair bond would be negatively correlated with rates of extra-pair paternity (EPP). Autosomal microsatellite analyses provide evidence for genetic monogamy in a pair-living primate with bi-parental care, the Azara''s owl monkey (Aotus azarae). A phylogenetically corrected generalized least square analysis was used to relate male care and strength of the pair bond to their genetic mating system (i.e. proportions of EPP) in 15 socially monogamous mammalian species. The intensity of male care was correlated with EPP rates in mammals, while strength of pair bond failed to reach statistical significance. Our analyses show that, once social monogamy has evolved, paternal care, and potentially also close bonds, may facilitate the evolution of genetic monogamy.  相似文献   

10.
The details of a cytogenetic study on 8 taxa of the mediterranean genus Anacyclus are presented. The results include information of the gross morphology, pollen fertilities and meiotic pairing behaviour of F1 hybrids supplemented by data on the karyotype morphology and DNA contents of parenthal plants. The results indicate that evolution in the genus has been accompanied by chromosomal repatterning. There are three distinctive groups within the experimental taxa, a pair of closely related perennials and two groups of annuals. There is considerable genome homology within each group but major differences between them. The groups are discussed in terms of their systematic relationships with other members of the genus in an effort to provide an explicit evolutionary model for the origin of different taxa. The understanding of the relationships of the annual taxa is complicated by sympatry and the occurrence of natural hybrids.  相似文献   

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