Human Mitochondrial DNA Variation and Evolution: Analysis of Nucleotide Sequences from Seven Individuals

We have analyzed nucleotide sequence variation in an approximately 900-base pair region of the human mitochondrial DNA molecule encompassing the heavy strand origin of replication and the D-loop. Our analysis has focused on nucleotide sequences available from seven humans. Average nucleotide diversity among the sequences is 1.7%, several-fold higher than estimates from restriction endonuclease site variation in mtDNA from these individuals and previously reported for other humans. This disparity is consistent with the rapidly evolving nature of this noncoding region. However, several instances of convergent or parallel gain and loss of restriction sites due to multiple substitutions were observed. In addition, other results suggest that restriction site (as well as pairwise sequence) comparisons may underestimate the total number of substitutions that have occurred since the divergence of two mtDNA sequences from a common ancestral sequence, even at low levels of divergence. This emphasizes the importance of recognizing the large standard errors associated with estimates of sequence variability, particularly when constructing phylogenies among closely related sequences. Analysis of the observed number and direction of substitutions revealed several significant biases, most notably a strand dependence of substitution type and a 32-fold bias favoring transitions over transversions. The results also revealed a significantly nonrandom distribution of nucleotide substitutions and sequence length variation. Significantly more multiple substitutions were observed than expected for these closely related sequences under the assumption of uniform rates of substitution. The bias for transitions has resulted in predominantly convergent or parallel changes among the observed multiple substitutions. There is no convincing evidence that recombination has contributed to the mtDNA sequence diversity we have observed.     

Mitochondrial DNA sequences of primates: Tempo and mode of evolution

Summary We cloned and sequenced a segment of mitochondrial DNA from human, chimpanzee, gorilla, orangutan, and gibbon. This segment is 896 bp in length, contains the genes for three transfer RNAs and parts of two proteins, and is homologous in all 5 primates. The 5 sequences differ from one another by base substitutions at 283 positions and by a deletion of one base pair. The sequence differences range from 9 to 19% among species, in agreement with estimates from cleavage map comparisons, thus confirming that the rate of mtDNA evolution in primates is 5 to 10 times higher than in nuclear DNA. The most striking new finding to emerge from these comparisons is that transitions greatly outnumber transversions. Ninety-two percent of the differences among the most closely related species (human, chimpanzee, and gorilla) are transitions. For pairs of species with longer divergence times, the observed percentage of transitions falls until, in the case of comparisons between primates and non-primates, it reaches a value of 45. The time dependence is probably due to obliteration of the record of transitions by multiple substitutions at the same nucleotide site. This finding illustrates the importance of choosing closely related species for analysis of the evolutionary process. The remarkable bias toward transitions in mtDNA evolution necessitates the revision of equations that correct for multiple substitutions at the same site. With revised equations, we calculated the incidence of silent and replacement substitutions in the two protein-coding genes. The silent substitution rate is 4 to 6 times higher than the replacement rate, indicating strong functional constraints at replacement sites. Moreover, the silent rate for these two genes is about 10% per million years, a value 10 times higher than the silent rate for the nuclear genes studied so far. In addition, the mean substitution rate in the three mitochondrial tRNA genes is at least 100 times higher than in nuclear tRNA genes. Finally, genealogical analysis of the sequence differences supports the view that the human lineage branched off only slightly before the gorilla and chimpanzee lineages diverged and strengthens the hypothesis that humans are more related to gorillas and chimpanzees than is the orangutan.Abbreviations mtDNA mitochondrial DNA - bp base pair - URF unidentified reading frame     

Man's place in hominoidea revealed by mitochondrial DNA genealogy

Summary Molecular biology has resurrected C. Darwin and T.H. Huxley's question about the origin of humans, but the precise branching pattern and dating remain controversial. To settle this issue, a large amount of sequence information is required. We determined mitochondrial (mt) DNA sequences for five hominoids; pygmy and common chimpanzees, gorilla, orangutan, and siamang. The common region compared with the known human sequence is 4759 by long, encompassing genes for 11 transfer RNAs and 6 proteins. Because of the high substitution rates in mammalian mtDNA and an unprecedentedly large region compared, the sequence differences clearly indicate that the closest relatives to human are chimpanzees rather than gorilla. For dating the divergences of human, chimpanzee, and gorilla, we used only unsaturated parts of sequence differences in which the mtDNA genealogy is not obscured by multiple substitutions. The result suggests that gorilla branched off 7.7 ± 0.7 million years (Myr) ago and human 4.7 ± 0.5 Myr ago; the time difference between these divergences being as long as 3 Myr.Offprint requests to: S. Horai     

Structure and evolution of the avian mitochondrial control region

The structural and evolutionary characteristics of the mitochondrial control region were studied by using control region sequences of 68 avian species. The distribution of the variable nucleotide positions within the control region was found to be genus specific and not dependant on the level of divergence, as suggested before. Saturation was shown to occur at the level of divergence of 10% in pairwise comparisons of the control region sequences, as has also been reported for the third codon positions in ND2 and cytochrome b genes of mtDNA. The ratio of control region vs cytochrome b divergence in pairwise comparisons of the sequences was shown to vary from 0.13 to 21.65, indicating that the control region is not always the most variable region of the mtDNA, but also that there are differences in the rate of divergence among the lineages. Only two of the conserved sequence blocks localized earlier for other species, D box and CSB-1, were found to show a considerable amount of sequence conservation across the avian and mammalian sequences. Additionally, a novel avian-specific sequence block was found.     

Evolutionary genetics of the suiformes as reconstructed using mtDNA sequencing

We have amplified and sequnced the entire mitochondrial DNA cytochromeb gene from four species of Suidae: babirusa, warthog, bearded pig, and some specimens belonging to different subspecies and populations of wild and domestic pigs (Sus scrofa). These sequences were aligned with additional mammalian sequences retrieved from the literature and were used to obtain phylogenetic trees of the Suiformes (Artiodactyla). Several species of Carnivora, Perissodactyla. Cetacea, and other Artiodactyla were used as outgroups. Molecular phylogenetic relationships among the Suiformes reflect their current taxonomy: Hippopotamidae, Tayassuidae, and Suidae are separated by deep genetic gaps, and the division of the Suidae into the subfamilies Babyrousinae., Phacochoerinae, and Suinae has strong genetic correlates. Cytochromeb sequences show differences among Asian and Western populations ofSus scrofa, agreeing with other genetic information (karyotypes blood groups, and protein variability). The two Italian subspecies of wild boar have unique mtDNA cytochromeb haplotypes. The evolutionary rates of cytochromeb sequences are different at transitions versus transversions as well as at first, second, and third positions of codons. Therefore, these classes of substitutions reached different levels of mutational saturation. Only transversions and the conservative first and second position substitutions are linearly related to genetic distances among the Suiformes. Therefore, divergence times were computed using unsaturated conserved nucleotide substitutions and calibrated using paleontological divergence times between some Artiodactyla. Transversions apparently evolve at remarkably regular rates in ungulate taxa which have accumulated less than 20% estimated sequence divergence, corresponding to about 40–45 million years of independent evolution. Molecular, information suggests that Hippopotamidae and Tayassuidae are not closely related (as stated by Pickford, 1986, 1989, 1993) and that the origin of babirusa and warthog (about 10–19 and 5–15 million years ago, respectively) is more recent than supported by current evolutionary reconstructions. The inferred origin of bearded pig is about 2.1 million years old, and genetic divergence among differentSus scrofa populations is probably a Pleistocene event. The addition of new sequences of Suiformes does not help in resolving the phylogenetic position ofHippopotamus amphibius, which shows weak but recurrent linkages with the cetacean evolutionary lineage.To whom correspondence should be addressed.     

Sequence Evolution of Drosophila Mitochondrial DNA

We have compared nucleotide sequences of corresponding segments of the mitochondrial DNA (mtDNA) molecules of Drosophila yakuba and Drosophila melanogaster, which contain the genes for six proteins and seven tRNAs. The overall frequency of substitution between the nucleotide sequences of these protein genes is 7.2%. As was found for mtDNAs from closely related mammals, most substitutions (86%) in Drosophila mitochondrial protein genes do not result in an amino acid replacement. However, the frequencies of transitions and transversions are approximately equal in Drosophila mtDNAs, which is in contrast to the vast excess of transitions over transversions in mammalian mtDNAs. In Drosophila mtDNAs the frequency of C----T substitutions per codon in the third position is 2.5 times greater among codons of two-codon families than among codons of four-codon families; this is contrary to the hypothesis that third position silent substitutions are neutral in regard to selection. In the third position of codons of four-codon families transversions are 4.6 times more frequent than transitions and A----T substitutions account for 86% of all transversions. Ninety-four percent of all codons in the Drosophila mtDNA segments analyzed end in A or T. However, as this alone cannot account for the observed high frequency of A----T substitutions there must be either a disproportionately high rate of A----T mutation in Drosophila mtDNA or selection bias for the products of A----T mutation. --Consideration of the frequencies of interchange of AGA and AGT codons in the corresponding D. yakuba and D. melanogaster mitochondrial protein genes provides strong support for the view that AGA specifies serine in the Drosophila mitochondrial genetic code.     

Sequence evolution and phylogenetic signal in control-region and cytochrome b sequences of rainbow fishes (Melanotaeniidae)

The nucleotide sequences of segments of the cytochrome b gene (351 bp), the tRNA(Pro) gene (49 bp), and the control region (approximately 313 bp) of mitochondrial DNA were obtained from 26 fish representing different populations and species of Melanotaenia and one species of Glossolepis, freshwater rainbow fishes confined to Australia and New Guinea. The purpose was to investigate relative rates and patterns of sequence evolution. Overall levels of divergence were similar for the cytochrome b and tRNA control-region sequences, both ranging from < 1% within subspecies to 15%-19% between genera. However, the patterns of sequence evolution differed. For the cytochrome b gene, transitions consistently exceeded transversions, the bias ranging from 4.2:1 to 2:1, depending on the level of sequence divergence. However, in the control-region sequence, a bias toward transitions (2:1) was observed only in comparisons between very similar sequences, and transversions outnumbered transitions in comparisons of divergent sequences. Graphic comparisons suggested that the control region was saturated for transitions at relatively low levels of sequence divergence but accumulated transversions at a greater rate than did the cytochrome b sequence. These distinct patterns of base substitution are associated with differences in A+T content, which is 70% for the tRNA control- region segment versus 50% for cytochrome b. A test for skewness in the distribution of lengths of random trees indicated that both segments contained phylogenetic signal. Parsimony analyses of the data from the two regions, with or without weighting schemes appropriate to the respective patterns of sequence evolution, identified the same five groupings of sequences, but the relationships among the groups differed. However, in most cases the branches uniting different combinations of groups were poorly supported, and the differences among topologies were insignificant. Considering the observed patterns of base substitution and the results of the phylogenetic analyses, we deduce that both the control region and cytochrome b are appropriate for population genetic studies but that the control region is less effective than cytochrome b for resolving relationships among divergent lineages of rainbow fishes.      

A Phylogenetic Study of the Origin of the Domestic Pig Estimated from the Near-Complete mtDNA Genome

The near-complete pig mtDNA genome sequence (15,997 bp) was determined from two domestic pigs (one Chinese Meishan and one Swedish Landrace) and two European wild boars. The sequences were analyzed together with a previously published sequence representing a Swedish domestic pig. The sequences formed three distinct clades, denoted A, E1, and E2, with considerable sequence divergence between them (0.8–1.2%). The results confirm our previous study (based on the sequence of the cytochrome B gene and the control region only) and provide compelling evidence that domestication of pigs must have occurred from both an Asian and a European subspecies of the wild boar. We estimated the time since the divergence of clade A (found in Chinese Meishan pigs) and E1 (found in European domestic pigs) at about 900,000 years before present, long before domestication about 9000 years ago. The pattern of nucleotide substitutions among the sequences was in good agreement with previous interspecific comparisons of mammalian mtDNA; the lowest substitution rates were observed at nonsynonymous sites in protein-coding genes, in the tRNA and rRNA genes, while the highest rates were observed at synonymous sites and in the control region. The presence of Asian clade A in some major European breeds (Large White and Landrace) most likely reflects the documented introgression of Asian germplasm into European stocks during the 18th and 19th centuries. The coexistence of such divergent mtDNA haplotypes for 100+ generations is expected to lead to the presence of recombinant haplotypes if paternal transmission and recombination occur at a low frequency. We found no evidence of such recombination events in the limited sample studied so far. Received: 19 April 2000; Accepted: 15 November 2000     

Analysis of nucleotide substitutions of mitochondrial DNAs in Drosophila melanogaster and its sibling species

To study the rate and pattern of nucleotide substitution in mitochondrial DNA (mtDNA), we cloned and sequenced a 975-bp segment of mtDNA from Drosophila melanogaster, D. simulans, and D. mauritiana containing the genes for three transfer RNAs and parts of two protein- coding genes, ND2 and COI. Statistical analysis of synonymous substitutions revealed a predominance of transitions over transversions among the three species, a finding differing from previous results obtained from a comparison of D. melanogaster and D. yakuba. The number of transitions observed was nearly the same for each species comparison, including D. yakuba, despite the differences in divergence times. However, transversions seemed to increase steadily with increasing divergence time. By contrast, nonsynonymous substitutions in the ND2 gene showed a predominance of transversions over transitions. Most transversions were between A and T and seemed to be due to some kind of mutational bias to which the A + T-rich mtDNA of Drosophila species may be subject. The overall rate of nucleotide substitution in Drosophila mtDNA appears to be slightly faster (approximately 1.4 times) than that of the Adh gene. This contrasts with the result obtained for mammals, in which the mtDNA evolves approximately 10 times faster than single-copy nuclear DNA. We have also shown that the start codon of the COI gene is GTGA in D. simulans and GTAA in D. mauritiana. These codons are different from that of D. melanogaster (ATAA).      

Evolution of glucagon genes

Statistical analyses of DNA sequences of the preproglucagon genes from bovine, human, hamster, and anglerfish suggest that a gene duplication creating two anglerfish genes (AF I and II) occurred about 160 Myr ago, long after the separation of fish and mammals. The analyses further suggest that the internal duplication producing the glucagon and glucagon-like peptide II (GLP-II) regions occurred about 1.2 billion years ago, which would indicate that the GLP-II region was present in the ancestral anglerfish sequence but was silenced or deleted before the gene duplication separating AF I and II. The glucagon-like peptide I (GLP-I) was derived from a duplication of the ancestral glucagon region about 800 Myr ago. The rate of synonymous substitution in these genes is approximately 4.3 x 10(-9) substitutions per year per synonymous site. The rate of nonsynonymous substitution in the signal peptide region is about 1.1 x 10(-9) substitutions per year per nonsynonymous site, a high rate comparable to that in the C-peptide region of preproinsulin. The rate of nonsynonymous substitution in the glicentin-related pancreatic polypeptide (GRPP) region is 0.63 x 10(-9) for the comparisons between mammalian species and 1.8 x 10(-9) for the comparisons between fish and mammals; the moderate rate in mammals suggests a physiological role for GRPP. The glucagon region is extremely conservative; no nonsynonymous substitution is observed in the mammalian genes, and a nonsynonymous rate of 0.18 x 10(-9) was obtained from the comparisons between fish and mammals. In the GLP-I region, the rate of nonsynonymous substitution was estimated to be 0.08 x 10(-9) for the comparisons between mammalian species and 0.30 x 10(- 9) for the comparisons between fish and mammals. In the GLP-II region, the rate was estimated to be 0.25 x 10(-9) for the comparisons between mammalian species. Thus, GLP-I and II are also very conservative, which suggests an important physiological role for these peptides.      

c-mos variation in songbirds: molecular evolution, phylogenetic implications, and comparisons with mitochondrial differentiation

Nucleotide sequences from the c-mos proto-oncogene have previously been used to reconstruct the phylogenetic relationships between distantly related vertebrate taxa. To explore c-mos variation at shallower levels of avian divergence, we compared c-mos sequences from representative passerine taxa that span a range of evolutionary differentiation, from basal passerine lineages to closely allied genera. Phylogenetic reconstructions based on these c-mos sequences recovered topologies congruent with previous DNA-DNA hybridization-based reconstructions, with many nodes receiving high support, as indicated by bootstrap and reliability values. One exception was the relationship of Acanthisitta to the remaining passerines, where the c-mos-based searches indicated a three-way polytomy involving the Acanthisitta lineage and the suboscine and oscine passerine clades. We also compared levels of c-mos and mitochondrial differentiation across eight oscine passerine taxa and found that c-mos nucleotide substitutions accumulate at a rate similar to that of transversion substitutions in mitochondrial protein-coding genes. These comparisons suggest that nuclear-encoded loci such as c-mos provide a temporal window of phylogenetic resolution that overlaps the temporal range where mitochondrial protein-coding sequences have their greatest utility and that c-mos substitutions and mtDNA transversions can serve as complementary, informative, and independent phylogenetic markers for the study of avian relationships.     

Mitochondrial DNA of the extinct quagga: Relatedness and extent of postmortem change

Sequences are reported for portions of two mitochondrial genes from a domestic horse and a plains zebra and compared to those published for a quagga and a mountain zebra. The extinct quagga and plains zebra sequences are identical at all silent sites, whereas the horse sequence differs from both of them by 11 silent substitutions. Postmortem changes in quagga DNA may account for the two coding substitutions between the quagga and plains zebra sequences. The hypothesis that the closest relative of the quagga is the domestic horse receives no support from these data. From the extent of sequence divergence between horse and zebra mitochondrial DNAs (mtDNAs), as well as from information about the fossil record, we estimate that the mean rate of mtDNA divergence in Equus is similar to that in other mammals, i.e., roughly 2% per million years.     

Molecular biogeography: using the Corsica-Sardinia microplate disjunction to calibrate mitochondrial rDNA evolutionary rates in mountain newts (Euproctus)

Mitochondrial DNA (mtDNA) sequence variation was examined in the three species belonging to the newt genus Euproctus: E. asper, E. montanus, and E. platycephalus, and in three other species belonging to the same family: Triturus carnifex, T. vulgaris and Pleurodeles waltl. The Euproctus species inhabit mountain streams in the Pyrenean region, Corsica, and Sardinia, respectively. This vicariant distribution is believed to be a result of the disjunction and rotation of the Sardinia-Corsica microplate from the Pyrenean region and suggested dates for each cladogenetic event are available. A total of 915 bp from 12S and 16S ribosomal rRNA genes were compared for each taxon. These are the first mt-rDNA sequence data for salamanders. Sequences were used to reconstruct phylogenetic trees, investigate evolutionary rates for these genes, calibrate them with absolute time since divergence, and compare rates with published ones. Using P. waltl as the outgroup, all phylogenetic methods used (parsimony, maximum likelihood, and Neighbor Joining) produced trees with identical topologies and similar bootstrap values associated with each node. These sequence data cannot unambiguously resolve the splitting events leading to the main radiation of the genus Triturus and the origin of the genus Euproctus. These events may well have occurred very close in time, consistent with other sorts of data. Although it is unlikely strict linearity holds for all kinds of substitutions, relative rate tests of the molecular clock hypothesis could not reject clock-like behavior of sequence changes along Euproctus lineages. Estimates of absolute rates of base changes are 0.35% per Myr since divergence for all substitutions and 0.14% per Myr for transversions; these estimates are similar to other vertebrate estimates. A comparison with distance measures from allozyme studies agrees quite well with regard to relative divergences of the three Euproctus species.     

Mitochondrial DNA evolution at a turtle's pace: evidence for low genetic variability and reduced microevolutionary rate in the Testudines.

Evidence is compiled suggesting a slowdown in mean microevolutionary rate for turtle mitochondrial DNA (mtDNA). Within each of six species or species complexes of Testudines, representing six genera and three taxonomic families, sequence divergence estimates derived from restriction assays are consistently lower than expectations based on either (a) the dates of particular geographic barriers with which significant mtDNA genetic clades appear associated or (b) the magnitudes of sequence divergence between mtDNA clades in nonturtle species that otherwise exhibit striking phylogeographic concordance with the genetic partitions in turtles. Magnitudes of the inferred rate slowdowns average eightfold relative to the "conventional" mtDNA clock calibration of 2%/Myr sequence divergence between higher animal lineages. Reasons for the postulated deceleration remain unknown, but two intriguing correlates are (a) the exceptionally long generation length most turtles and (b) turtles' low metabolic rate. Both factors have been suspected of influencing evolutionary rates in the DNA sequences of some other vertebrate groups. Uncertainities about the dates of cladogenetic events in these Testudines leave room for alternatives to the slowdown interpretation, but consistency in the direction of the inferred pattern, across several turtle species and evolutionary settings, suggests the need for caution in acceptance of a universal mtDNA-clock calibration for higher animals.     

Increased genetic diversity in mitochondrial genes is correlated with the evolution of parasitism in the Hymenoptera

A higher AT content and rate of mtDNA sequence divergence was found in parasitic wasps (Apocrita) compared with nonparasitic wasps (Symphyta). The compositional bias was reflected in extreme codon bias for a cytochrome oxidase I protein coding gene fragment as well as in the types of amino acid substitutions that have occurred during the evolution of this gene fragment. In some instances, compositional bias influenced the definition of a conservative amino acid change. The increased rate of mtDNA sequence evolution probably arose during the early Jurassic, coincident with the first appearance of parasitic wasps in the fossil record. Our results suggest a causal link between the rate of sequence divergence and the parasitic lifestyle.Abbreviations AT adenosine-thymine - CO-1 cytochrome oxidase 1 - mtDNA mitochondrial DNA - Myr million years Correspondence to: M. Dowton     

Mitochondrial DNA evolution in the genus Equus

Employing mitochondrial DNA (mtDNA) restriction-endonuclease maps as the basis of comparison, we have investigated the evolutionary affinities of the seven species generally recognized as the genus Equus. Individual species' cleavage maps contained an average of 60 cleavage sites for 16 enzymes, of which 29 were invariant for all species. Based on an average divergence rate of 2%/Myr, the variation between species supports a divergence of extant lineages from a common ancestor approximately 3.9 Myr before the present. Comparisons of cleavage maps between Equus przewalskii (Mongolian wild horse) and E. caballus (domestic horse) yielded estimates of nucleotide sequence divergence ranging from 0.27% to 0.41%. This range was due to intraspecific variation, which was noted only for E. caballus. For pairwise comparisons within this family, estimates of sequence divergence ranged from 0% (E. hemionus onager vs. E. h. kulan) to 7.8% (E. przewalskii vs. E. h. onager). Trees constructed according to the parsimony principle, on the basis of 31 phylogenetically informative restriction sites, indicate that the three extant zebra species represent a monophyletic group with E. grevyi and E. burchelli antiquorum diverging most recently. The phylogenetic relationships of E. africanus and E. hemionus remain enigmatic on the basis of the mtDNA analysis, although a recent divergence is unsupported.      

Pancreatic-Type Ribonuclease 1 Gene Duplications in Rat Species

Mammalian pancreatic-type ribonucleases (RNases) 1 represent single-copy genes in the genome of most investigated mammalian species, including Mus musculus and other murid rodents. However, in six species belonging to the genus Rattus and closely related taxa, several paralogous gene products were identified by Southern blotting and PCR amplifications of genomic sequences. Phylogenies of nucleotide and derived amino acid sequences were reconstructed by several procedures, with three Mus species as outgroup. Duplications of the RNase 1 occurred after the divergence of Niviventer cremoriventer and Leopoldamys edwardsi from the other investigated species. Four groups of paralogous genes could be identified from specific amino acid sequence features in each of them. Low ratios of nonsynonymous-to-synonymous substitutions and the paucity of pseudogene features suggest functional gene products. One of the RNase 1 genes of R. norvegicus is expressed in the pancreas. RNases 1 were isolated from pancreatic tissues of R. rattus and R. exulans and submitted to N-terminal amino acid sequence analysis. In R. rattus, the orthologue of the expressed gene of R. norvegicus was identified, but in R. exulans, two paralogous gene products were found. The gene encoding for one of these had not yet been found by PCR amplification of genomic DNA. A well-defined group of orthologous sequences found in five investigated species codes for very basic RNases. Northern blot analysis showed expression of messenger RNA for this RNase in the spleen of R. norvegicus, but the protein product could not be identified. Evolutionary rates of RNase 1, expressed as nucleotide substitutions per site per 10(3) million years (Myr), vary between 5 and 9 in the lines leading to Mus, Niviventer, and Lepoldamys (on the basis of an ancestral date of mouse/rat divergence of 12.2 Myr) and between 20 and 50 in the lines to the other sequences after divergence from Niviventer and Leopoldamys (5.5 Myr).     

小口白甲鱼都柳江种群mtDNA D环的序列变异及遗传多样性

采用PCR结合DNA测序技术,测定分析了易危鱼类小口白甲鱼(Onychostoma lini)都柳江种群36个个体mtDNA D环约470bp序列的变异及遗传多样性。结果表明,在36个个体中,该序列的长度为469～475bp,其碱基组成为A+T的平均含量(68.4%)高于G+C(31.6%)。共检测到25个多态位点,其中转换19个、颠换6个。核苷酸多样性(π)为0.00575,平均核苷酸差异数(K)为2.695。36个个体分属5个单倍型,单倍型多样度(Hd)为0.260,单倍型间的平均遗传距离(P)为0.026。5个单倍型构建的UPGMA系统树聚为2个分支。目前小口白甲鱼都柳江种群mtDNA D环序列存在着较丰富的变异和遗传多样性。     

Comparison of mitochondrial DNA in two greenling species and their hybrids (CEM. Hexagrammidae: Pisces) from Peter the Great Bay (Sea of Japan)]

Fragments of mtDNA from two greenling species, Hexagrammos octogrammus and H. agrammus, and their possible hybrids were amplified in PCR and examined using RFLP analysis. The inferred sequence difference between the species was 6.6%, which corresponds to about 3 Myr of their divergence. The reproductive contribution of males and females to the hybrids was estimated.