Error-reducing Structure of the Genetic Code Indicates Code Origin in Non-thermophile Organisms

During the RNA World, organisms experienced high rates of genetic errors, which implies that there was strong evolutionary pressure to reduce the errors’ phenotypical impact by suitably structuring the still-evolving genetic code. Therefore, the relative rates of the various types of genetic errors should have left characteristic imprints in the structure of the genetic code. Here, we show that, therefore, it is possible to some extent to reconstruct those error rates, as well as the nucleotide frequencies, for the time when the code was fixed. We find evidence indicating that the frequencies of G and C in the genome were not elevated. Since, for thermodynamic reasons, RNA in thermophiles tends to possess elevated G+C content, this result indicates that the fixation of the genetic code occurred in organisms which were either not thermophiles or that the code’s fixation occurred after the rise of DNA. Supplementary Materials Original data and programs are available at the author’s web site: .     

Signature of a Primitive Genetic Code in Ancient Protein Lineages

The genetic code is the syntactic foundation underlying the structure and function of every protein in the history of the biological world. Its highly ordered degenerate complexity suggests an incremental evolution, the result of a combination of selective, mechanistic, and random processes. These evolutionary processes are still poorly understood and remain an open question in the study of early life on Earth. We perform a compositional analysis of ribosomal proteins and ATPase subunits in bacterial and archaeal lineages, using conserved positions that came and remained under purifying selection before and up to the most recent common ancestor. An observable shift in amino acid usage at these conserved positions likely provides an untapped window into the history of protein sequence space, allowing events of genetic code expansion to be identified. We identify Cys, Glu, Phe, Ile, Lys, Val, Trp, and Tyr as recent additions to the genetic code, with Asn, Gln, Gly, and Leu among the more ancient. Our observations are consistent with a scenario in which genetic code expansion primarily favored amino acids that promoted an increase in polypeptide size and functionality. We propose that this expansion would have been critical in the takeover of many RNA-mediated processes, as well as the addition of novel biological functions inaccessible to an RNA-based physiology, such as crossing lipid membranes. Thus, expansion of the genetic code likely set the stage for the transition from RNA-based to protein-based life. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A Novel Theory on the Origin of the Genetic Code: A GNC-SNS Hypothesis

We have previously proposed an SNS hypothesis on the origin of the genetic code (Ikehara and Yoshida 1998). The hypothesis predicts that the universal genetic code originated from the SNS code composed of 16 codons and 10 amino acids (S and N mean G or C and either of four bases, respectively). But, it must have been very difficult to create the SNS code at one stroke in the beginning. Therefore, we searched for a simpler code than the SNS code, which could still encode water-soluble globular proteins with appropriate three-dimensional structures at a high probability using four conditions for globular protein formation (hydropathy, α-helix, β-sheet, and β-turn formations). Four amino acids (Gly [G], Ala [A], Asp [D], and Val [V]) encoded by the GNC code satisfied the four structural conditions well, but other codes in rows and columns in the universal genetic code table do not, except for the GNG code, a slightly modified form of the GNC code. Three three-amino acid systems ([D], Leu and Tyr; [D], Tyr and Met; Glu, Pro and Ile) also satisfied the above four conditions. But, some amino acids in the three systems are far more complex than those encoded by the GNC code. In addition, the amino acids in the three-amino acid systems are scattered in the universal genetic code table. Thus, we concluded that the universal genetic code originated not from a three-amino acid system but from a four-amino acid system, the GNC code encoding [GADV]-proteins, as the most primitive genetic code. Received: 11 June 2001 / Accepted: 11 October 2001     

A Blind Empiricism Against the Coevolution Theory of the Origin of the Genetic Code

Ronneberg et al. (Proc Natl Acad Sci USA 97:13690–13695, 2000) recently suggested abandoning the coevolution theory of genetic code origin on the basis of two pieces of evidence. They (1) criticize the use of several pairs of amino acids in a precursor–product relationship to support this theory and (2) suggest a new set of codes in which to investigate the statistical bases of the coevolution theory, reaching the conclusion that this theory is not statistically validated in this set. In this paper I critically analyze the robustness of these conclusions. Observations and arguments lead to the belief that the pairs of amino acids in a precursor–product relationship originally used by the coevolution theory are such, or may at least be interpreted as such, and are therefore a manifestation of this theory. Furthermore, the new set of codes that Ronneberg et al. suggest is open to criticism and is thus substituted by the set of amino acid permutation codes, in which even the pairs of amino acids they favor end up by supporting the coevolution theory. Overall, the analysis seems to show that the paper by Ronneberg et al. is of minor scientific value while the coevolution theory seems to be one of the best theories at our disposal for explaining the evolutionary organisation of the genetic code and is, contrary to their claims, statistically well validated. Received: 21 February 2001 / Accepted: 22 May 2001     

Relationships Among Isoacceptor tRNAs Seems to Support the Coevolution Theory of the Origin of the Genetic Code

A new method for looking at relationships between nucleotide sequences has been used to analyze divergence both within and between the families of isoaccepting tRNA sets. A dendrogram of the relationships between 21 tRNA sets with different amino acid specificities is presented as the result of the analysis. Methionine initiator tRNAs are included as a separate set. The dendrogram has been interpreted with respect to the final stage of the evolutionary pathway with the development of highly specific tRNAs from ambiguous molecular adaptors. The location of the sets on the dendrogram was therefore analyzed in relation to hypotheses on the origin of the genetic code: the coevolution theory, the physicochemical hypothesis, and the hypothesis of ambiguity reduction of the genetic code. Pairs of 16 sets of isoacceptor tRNAs, whose amino acids are in biosynthetic relationships, occupied contiguous positions on the dendrogram, thus supporting the coevolution theory of the genetic code. Received: 4 May 1998 / Accepted: 11 July 1998     

An Analytical Model of Gene Evolution with 9 Mutation Parameters: An Application to the Amino Acids Coded by the Common Circular Code

We develop here an analytical evolutionary model based on a trinucleotide mutation matrix 64× 64 with nine substitution parameters associated with the three types of substitutions in the three trinucleotide sites. It generalizes the previous models based on the nucleotide mutation matrices 4× 4 and the trinucleotide mutation matrix 64× 64 with three and six parameters. It determines at some time t the exact occurrence probabilities of trinucleotides mutating randomly according to these nine substitution parameters. An application of this model allows an evolutionary study of the common circular code of eukaryotes and prokaryotes and its 12 coded amino acids. The main property of this code is the retrieval of the reading frames in genes, both locally, i.e. anywhere in genes and in particular without a start codon, and automatically with a window of a few nucleotides. However, since its identification in 1996, amino acid information coded by has never been studied. Very unexpectedly, this evolutionary model demonstrates that random substitutions in this code and with particular values for the nine substitutions parameters retrieve after a certain time of evolution a frequency distribution of these 12 amino acids very close to the one coded by the actual genes.     

Ribonucleotide reductases and their occurrence in microorganisms: A link to the RNA/DNA transition

Abstract: The evolution of a deoxyribonucleotide synthesizing ribonucleotide reductase might have initiated the transition from the ancient RNA world into the prevailing DNA world. At least five classes of ribonucleotide reductases have evolved. The ancient enzyme has not been identified. A reconstruction of the first ribonucleotide reductase requires knowledge of contemporary enzymes and of microbial evolution. Experimental work on the former focuses on few organisms, whereas the latter is now well understood on the basis of ribosomal RNA sequences. Deoxyribonucleotide formation has not been investigated in many evolutionary important microorganisms. This review covers our knowledge on deoxyribonucleotide synthesis in microorganisms and the distribution of ribonucleotide reductases in nature. Ecological constraints on enzyme evolution and knowledge deficiencies emerge from complete coverage of the phylogenetic groups.     

On the Structural Regularity in Nucleobases and Amino Acids and Relationship to the Origin and Evolution of the Genetic Code

To explore how chemical structures of both nucleobases and amino acids may have played a role in shaping the genetic code, numbers of sp² hybrid nitrogen atoms in nucleobases were taken as a determinative measure for empirical stereo-electronic property to analyze the genetic code. Results revealed that amino acid hydropathy correlates strongly with the sp² nitrogen atom numbers in nucleobases rather than with the overall electronic property such as redox potentials of the bases, reflecting that stereo-electronic property of bases may play a role. In the rearranged code, five simple but stereo-structurally distinctive amino acids (Gly, Pro, Val, Thr and Ala) and their codon quartets form a crossed intersection “core”. Secondly, a re-categorization of the amino acids according to their β-carbon stereochemistry, verified by charge density (at β-carbon) calculation, results in five groups of stereo-structurally distinctive amino acids, the group leaders of which are Gly, Pro, Val, Thr and Ala, remarkably overlapping the above “core”. These two lines of independent observations provide empirical arguments for a contention that a seemingly “frozen” “core” could have formed at a certain evolutionary stage. The possible existence of this codon “core” is in conformity with a previous evolutionary model whereby stereochemical interactions may have shaped the code. Moreover, the genetic code listed in UCGA succession together with this codon “core” has recently facilitated an identification of the unprecedented icosikaioctagon symmetry and bi-pyramidal nature of the genetic code.     

Bacteriophage MS2 RNA: A correlation between the stability of the codon: Anticodon interaction and the choice of code words

Summary The non-random distribution of degenerate code words in Bacteriophage MS2 RNA can be explained partially by considerations of the stability of the codon-anticodon complex in prokaryotic systems. Supporting this hypothesis we note that wobble codons are positively selected in codons having G and/or C in the first two positions. In contrast, wobble codons are statitically less likely in codons composed of A and U in the first two positions. Analyses of nucleotides adjacent to 5 and 3 ends of codons indicate a nonrandom distribution as well. It is thus likely that some elements of RNA evolution are independent of the structural needs of the RNA itself and of the translated protein product.This work was supported by grants from the Belgian Government Actions concertées - Gekon-certéerde Acties, N.F.W.O. and F.K.F.O. as well as from le Ministère de l'éducation du Québec. A preliminary report of this work was given at the EMBO ribosome workshop, Brussels 1976     

Stability of the genetic code and optimal parameters of amino acids

The standard genetic code is known to be much more efficient in minimizing adverse effects of misreading errors and one-point mutations in comparison with a random code having the same structure, i.e. the same number of codons coding for each particular amino acid. We study the inverse problem, how the code structure affects the optimal physico-chemical parameters of amino acids ensuring the highest stability of the genetic code. It is shown that the choice of two or more amino acids with given properties determines unambiguously all the others. In this sense the code structure determines strictly the optimal parameters of amino acids or the corresponding scales may be derived directly from the genetic code. In the code with the structure of the standard genetic code the resulting values for hydrophobicity obtained in the scheme “leave one out” and in the scheme with fixed maximum and minimum parameters correlate significantly with the natural scale. The comparison of the optimal and natural parameters allows assessing relative impact of physico-chemical and error-minimization factors during evolution of the genetic code. As the resulting optimal scale depends on the choice of amino acids with given parameters, the technique can also be applied to testing various scenarios of the code evolution with increasing number of codified amino acids. Our results indicate the co-evolution of the genetic code and physico-chemical properties of recruited amino acids.     

An Extended Model for the Evolution of Prebiotic Homochirality: A Bottom-Up Approach to the Origin of Life

A generalized autocatalytic model for chiral polymerization is investigated in detail. Apart from enantiomeric cross-inhibition, the model allows for the autogenic (non-catalytic) formation of left and right-handed monomers from a substrate with reaction rates epsilon L and epsilon R, respectively. The spatiotemporal evolution of the net chiral asymmetry is studied for models with several values of the maximum polymer length, N. For N = 2, we study the validity of the adiabatic approximation often cited in the literature. We show that the approximation obtains the correct equilibrium values of the net chirality, but fails to reproduce the short time behavior. We show also that the autogenic term in the full N = 2 model behaves as a control parameter in a chiral symmetry-breaking phase transition leading to full homochirality from racemic initial conditions. We study the dynamics of the N--> infinity model with symmetric (epsilon L = epsilon R) autogenic formation, showing that it only achieves homochirality for epsilon > epsilon c, where epsilon c is an N-dependent critical value. For epsilon 相似文献   

RNA结合蛋白与RNA互作鉴定技术

RNA结合蛋白（RNA binding proteins,RBPs）通过与RNA相互作用,广泛参与到RNA的剪切、转运、编辑、胞内定位及翻译调控等过程中。RNA领域尤其是非编码RNA（non-coding RNA,ncRNA）研究的快速发展,催生了多种RBPs RNAs相互作用鉴定技术。这些技术反之又推动了 RNA领域的研究进程。本文对紫外交联免疫沉淀（ultraviolet crosslinking and immunoprecipitation,CLIP）,CLIP cDNA文库高通量测序 (high-throughput sequencing of CLIP cDNA library,HITS-CLIP),光活化核苷增强的CLIP(photoactivatable-ribonucleoside-enhanced crosslinking and immunoprecipitation,PAR-CLIP),单核苷酸分离CLIP (individual nucleotide resolution CLIP,iCLIP),TRIBE (targets of RNA-binding protein identified by editing),RNA 标记,相互作用组捕获(interactome capture,IC) 和SerIC (serial RNA interactome capture)等RBPs-RNAs相互作用鉴定技术的基本原理和优缺点以及应用进行综述。     

tRNA genes and the genetic code

The genetic code describes translational assignments between codons and amino acids. tRNAs and aminoacyl-tRNA synthetases (aaRSs) are those molecules by means of which these assignments are established. Any aaRS recognizes its tRNAs according to some of their nucleotides called identity elements (IEs). Let a 1Mut-similarity Sim (1Mut) be the average similarity between such tRNA genes whose codons differ by one point mutation. We showed that: (1) a global maximum of Sim (1Mut) is reached at the standard genetic code 27 times for 4 sets of IEs of tRNA genes of eukaryotic species, while it is so only 5 times for similarities Sim (C&R) between all tRNA genes whose codons lie in the same column or row of the code. Therefore, point mutations of anticodons were tested by nature to recruit tRNAs from one isoaccepting group to another, (2) because plain similarities Sim (all) between tRNA genes of species within any of the three domains of life are higher than between tRNA genes of species belonging to different domains, tRNA genes retained information about early evolution of cells, (3) we searched the order of tRNAs in which they were most probably assigned to their codons and amino acids. The beginning Ala, (Val), Pro, Ile, Lys, Arg, Trp, Met, Asp, Cys, (Ser) of our resulting chronology lies under a plateau on a graph of Sim (1Mut,IE)(univ.ancestors) plotted over this chronology for a set S(IE) of all IEs of tRNA genes, whose universal ancestors were separately computed for each codon. This plateau has remained preserved along the whole line of evolution of the code and is consistent with observations of Ribas de Pouplana and Schimmel [2001. Aminoacy1-tRNA synthetases: potential markers of genetic code development. Trends Biochem. Sci. 26, 591-598] that specific pairs of aaRSs-one from each of their two classes-can be docked simultaneously onto the acceptor stem of tRNA and hence an interaction existed between their ancestors using a reduced code, (4) sharpness of a local maximum of Sim (1Mut) at the standard code is almost 100% along our chronologies.     

Gene duplication and other evolutionary strategies: from the RNA world to the future

Beginning with a hypothetical RNA world, it is apparent that many evolutionary transitions led to the complexity of extant species. The duplication of genetic material is rooted in the RNA world. One of two major routes of gene amplification, retroposition, originated from mechanisms that facilitated the transition to DNA as hereditary material. Even in modern genomes the process of retroposition leads to genetic novelties including the duplication of protein and RNA coding genes, as well as regulatory elements and their juxtapositon. We examine whether and to what extent known evolutionary principles can be applied to an RNA-based world. We conclude that the major basic Neo-Darwinian principles that include amplification, variation and selection already governed evolution in the RNA and RNP worlds. In this hypothetical RNA world there were few restrictions on the exchange of genetic material and principles that acted as borders at later stages, such as Weismann's Barrier, the Central Dogma of Molecular Biology, or the Darwinian Threshold were absent or rudimentary. RNA was more than a gene: it had a dual role harboring, genotypic and phenotypic capabilities, often in the same molecule. Nuons, any discrete nucleic acid sequences, were selected on an individual basis as well as in groups. The performance and success of an individual nuon was markedly dependent on the type of other nuons in a given cell. In the RNA world the transition may already have begun towards the linkage of nuons to yield a composite linear RNA genome, an arrangement necessitating the origin of RNA processing. A concatenated genome may have curbed unlimited exchange of genetic material; concomitantly, selfish nuons were more difficult to purge. A linked genome may also have constituted the beginning of the phenotype/genotype separation. This division of tasks was expanded when templated protein biosynthesis led to the RNP world, and more so when DNA took over as genetic material. The aforementioned barriers and thresholds increased and the significance and extent of horizontal gene transfer fluctuated over major evolutionary transitions. At the dawn of the most recent transformation, a fast evolutionary transition that we will be witnessing in our life times, a form of Lamarckism is raising its head.     

Looking for Progenitors: A Molecular Approach to Finding the Origins of An Invasive Weed

One of the major problems in determining the origin of invasive species is that often their arrival is unnoticed. Only when population levels increase is their presence noticed but by this time determining the point of arrival is confounded by the extensive spread of the species. Here we use molecular markers (ISSRs) to determine the origin of an invasive weed in the Kalahari region, a species for which several origins could be possible. We show that molecular markers can be useful tools in determining the origin of invasive species     

The influence of glucocorticoid on albumin synthesis and its messenger RNA in rat in vivo and in hepatocyte suspension culture

Corticosteroids are known to stimulate the synthesis of a number of liver-specific proteins. The reports regarding the effect of glucocorticoid on albumin synthesis in vivo and in vitro are controversial. In an attempt to determine the mechanism by which glucocorticoid exerts its influence on hepatic albumin synthesis and to find an explanation for the conflicting data, we have studied the effect of dexamethasone disodium phosphate on albumin synthesis and albumin messenger RNA as determined by the molecular hybridization technique in hepatocytes in rat in vivo and in suspension culture. In hepatocyte suspension culture, addition of 0.48 μM dexamethasone in medium at zero time led to a significant increase (20%) in incorporation of labeled precursor into albumin as compared to control experiments; this was accompanied by a maintainance of the initial level of full-length albumin mRNA for a 9 h period. In hepatocytes cultured without dexamethasone in the medium there was a progressive loss of albumin mRNA content. Despite this finding, dexamethasone was not able to increase the albumin mRNA content in hepatocyte to a level higher than the initial value. Moreover, administration of this hormone either intraperitoneally or intravenously into rats did not lead to enhanced cell-free albumin synthesis or to an increased level of albumin mRNA. These findings suggest that glucocorticoid does not play an essential role in the regulation of albumin synthesis in vivo. In vitro, however, glucocorticoid leads to a preservation of the initial level of albumin mRNA and thus plays a role in the control of spontaneous dedifferentiation of liver cells in culture.     

西双版纳傣族热带雨林生态文化及成因的探讨

西双版纳地处我国滇南,与缅甸、老挝接壤,邻近越南、泰国和柬埔寨。傣族是该地区的主体民族,跨国境而居。在近代,学者们对傣族传统文化有多种表述,但经作者比较与分析认为西双版纳傣族传统文化的属性应是热带雨林生态文化。热带雨林的生态系统多样性、生态景观独特性和物种多样性等与傣族的日常生活、医药卫生、生产活动、文学艺术和宗教信仰等关系十分密切,是雨林文化形成的根基。原始多神教和佛教的宗教信仰使傣族传统文化得到升华,是其核心。而地区内外的文化交流则使雨林文化得到发展与不断完善。     

Changes in RNA Synthesis and Messenger RNA Content in the Cerebellum of Rats with Graft Versus Host Disease

Cerebellar RNA accumulation, synthesis, and functional capacity was studied in 14-day-old F1 hybrid rats subjected to neonatally induced graft versus host disease (GVHD). There was a decrease in RNA synthetic rate as measured by the uptake of labeled precursors into RNA. The decrease in total cerebellar RNA synthesis was reflected both in a reduced amount of Nissl substance, visible in cresyl violet-stained 10-micron-thick sections of cerebella, and in the total amount of cytoplasmic RNA isolated from individual cerebella from diseased animals compared with control littermates. Analysis of the RNA translational capacity in wheat germ protein synthesizing systems showed that RNA from experimental animals was also biologically less active. Qualitative differences between protein populations in control and diseased animals were analyzed by two-dimensional gel electrophoresis. There were few alterations in the steady state levels of cerebellar protein. However, two-dimensional gel electrophoresis of the peptides synthesized in vitro by RNA from control and diseased animals showed that there were several changes in the relative abundance of some mRNAs between the two RNA populations. These data show that the cerebellar RNA from rats with GVHD differs both qualitatively and quantitatively from that of controls.     

Obcells as Proto-Organisms: Membrane Heredity, Lithophosphorylation, and the Origins of the Genetic Code, the First Cells, and Photosynthesis

I attempt to sketch a unified picture of the origin of living organisms in their genetic, bioenergetic, and structural aspects. Only selection at a higher level than for individual selfish genes could power the cooperative macromolecular coevolution required for evolving the genetic code. The protein synthesis machinery is too complex to have evolved before membranes. Therefore a symbiosis of membranes, replicators, and catalysts probably mediated the origin of the code and the transition from a nucleic acid world of independent molecular replicators to a nucleic acid/protein/lipid world of reproducing organisms. Membranes initially functioned as supramolecular structures to which different replicators attached and were selected as a higher-level reproductive unit: the proto-organism. I discuss the roles of stereochemistry, gene divergence, codon capture, and selection in the code's origin. I argue that proteins were primarily structural not enzymatic and that the first biological membranes consisted of amphipathic peptidyl-tRNAs and prebiotic mixed lipids. The peptidyl-tRNAs functioned as genetically-specified lipid analogues with hydrophobic tails (ancestral signal peptides) and hydrophilic polynucleotide heads. Protoribosomes arose from two cooperating RNAs: peptidyl transferase (large subunit) and mRNA-binder (small subunit). Early proteins had a second key role: coupling energy flow to the phosphorylation of gene and peptide precursors, probably by lithophosphorylation by membrane-anchored kinases scavenging geothermal polyphosphate stocks. These key evolutionary steps probably occurred on the outer surface of an `inside out-cell' or obcell, which evolved an unambiguous hydrophobic code with four prebiotic amino acids and proline, and initiation by isoleucine anticodon CAU; early proteins and nucleozymes were all membrane-attached. To improve replication, translation, and lithophosphorylation, hydrophilic substrate-binding and catalytic domains were later added to signal peptides, yielding a ten-acid doublet code. A primitive proto-ecology of molecular scavenging, parasitism, and predation evolved among obcells. I propose a new theory for the origin of the first cell: fusion of two cup-shaped obcells, or hemicells, to make a protocell with double envelope, internal genome and ribosomes, protocytosol, and periplasm. Only then did water-soluble enzymes, amino acid biosynthesis, and intermediary metabolism evolve in a concentrated autocatalytic internal cytosolic soup, causing 12 new amino acid assignments, termination, and rapid freezing of the 22-acid code. Anticodons were recruited sequentially: GNN, CNN, INN, and *UNN. CO₂ fixation, photoreduction, and lipid synthesis probably evolved in the protocell before photophosphorylation. Signal recognition particles, chaperones, compartmented proteases, and peptidoglycan arose prior to the last common ancestor of life, a complex autotrophic, anaerobic green bacterium. Received: 19 February 2001 / Accepted: 9 April 2001     

Genetic diversity and differentiation of Daphnia galeata in the middle and lower reaches of the Yangtze River,China

Mitochondrial 16S rDNA and CO I gene were used as molecular markers for the analysis of the genetic diversity and differentiation of Daphnia galeata populations in nine water bodies in the middle and lower reaches of the Yangtze River. In the combined 16S rDNA and CO I gene sequences, 54 variable sites and 44 haplotypes were observed among 219 individuals belonging to nine D. galeata populations. Average haplotype diversity and nucleotide diversity were, respectively, 0.72% and 0.56%. The F‐statistics (F_ST) value of the D. galeata populations was 0.149. According to the results of the neutral test, D. galeata in the middle and lower reaches of the Yangtze River had experienced a bottleneck effect in the history. Molecular variance analysis indicated that the genetic differentiation of the D. galeata populations mainly occurred within populations (85.09%). Greater genetic differentiations of D. galeata among individuals within populations appeared in the populations from the Huaihe River basin, whereas smaller genetic differentiations occurred in the populations from the middle reaches of the Yangtze River. Strong gene flows were all observed between Group I (four populations from the middle reaches of the Yangtze River) and Group ΙΙ (three populations from the middle and lower reaches of the Yangtze River), and Group ΙΙΙ (two populations from the Huaihe River basin). The effective migration rates (M) were 851.49 from Group I to Group ΙΙ and 685.96 from Group I to Group ΙΙΙ, respectively. However, no significant relationship was observed between the genetic differentiation and geographical distance of the nine populations (r = .137, p > .05). Results suggested that the genetic differentiation of D. galeata in the water bodies in the middle and lower reaches of the Yangtze River resulted mainly from geographical isolation.