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81.
Patterns of nucleotide change in mitochondrial ribosomal RNA genes and the phylogeny of piranhas 总被引:14,自引:0,他引:14
Guillermo Ortí Paulo Petry Jorge I. R. Porto Michel Jégu Axel Meyer 《Journal of molecular evolution》1996,42(2):169-182
The patterns and rates of nucleotide substitution in mitochondrial ribosomal RNA genes are described and applied in a phylogenetic analysis of fishes of the subfamily Serrasalminae (Teleostei, Characiformes, Characidae). Fragments of 345 bp of the 12S and 535 bp of the 16S genes were sequenced for 37 taxa representing all but three genera in the subfamily. Secondary-structure models based on comparative sequence analysis were derived to characterize the pattern of change among paired and unpaired nucleotides, forming stem and loop regions, respectively. Base compositional biases were in the direction of A-rich loops and G-rich stems. Ninety-five percent of substitutions in stem regions were compensatory mutations, suggesting that selection for maintenance of base pairing is strong and that independence among characters cannot be assumed in phylogenetic analyses of stem characters. The relative rate of nucleotide substitution was similar in both fragments sequenced but higher in loop than in stem regions. In both genes, C-T transitions were the most common type of change, and overall transitions outnumbered transversions by a factor of two in 16S and four in 12S. Phylogenetic analysis of the mitochondrial DNA sequences suggests that a clade formed by the generaPiaractus, Colossoma, andMylossoma is the sister group to all other serrasalmins and that the generaMyleus, Serrasalmus, andPristobrycon are paraphyletic. A previous hypothesis concerning relationships for the serrasalmins, based on morphological evidence, is not supported by the molecular data. However, phylogenetic analysis of host-specific helminth parasites and cytogenetic data support the phylogeny of the Serrasalminae obtained in this study and provide evidence for coevolution between helminth parasites and their fish hosts. 相似文献
82.
The complete mitochondrial DNA (mtDNA) of the donkey and mtDNA comparisons among four closely related mammalian species-pairs 总被引:7,自引:0,他引:7
The nucleotide sequence of the complete mitochondrial genome of the donkey, Equus asinus, was determined. The length of the molecule is 16,670 bp. The length, however, is not absolute due to pronounced heteroplasmy
caused by variable numbers of two types of repetitive motifs in the control region. The sequence of the repeats is (a) 5′-CACACCCA
and (b) 5′-TGCGCGCA, respectively. The order of (a) and (b) can be expressed as {n[2(a)+(b)]+m(a)}. In 32 different clones analyzed the number of n and m ranged from 0 to 9 and 1 to 7. The two rRNA genes, the 13 peptide-coding genes, and the 22 tRNA genes of the donkey and the
horse, Equus caballus, were compared in detail. Total nucleotide difference outside the control region was 6.9%. Nucleotide difference between peptide-coding
genes ranged from 6.4% to 9.4% with a mean of 8.0%. In the inferred protein sequences of the 13 peptide-coding genes the amino
acid difference was 0.2–8.8%, and the mean for the 13 concatenated amino acid sequences was 1.9%. In the 22 tRNA genes, the
mean difference was 3.5%, and that in the two rRNA genes was 4.1%. The mtDNA differences between the donkey and the horse
suggest that the evolutionary separation of the two species occurred ≈9 million years ago. Analyses of differences among the
mtDNAs of three other species-pairs, harbor seal/grey seal, fin whale/blue whale, and Homo/common chimpanzee, showed that the relative evolutionary rate of individual peptide-coding genes varies among different species-pairs
and modes of comparison. The findings show that the superimposition of sequence data of one lineage for resolving and dating
evolutionary divergences of other lineages should be performed with caution unless based on comprehensive data.
Received: 15 October 1995 / Accepted: 15 April 1996 相似文献
83.
84.
Development of microsatellite markers and characterization of simple sequence length polymorphism (SSLP) in rice (Oryza sativa L.) 总被引:26,自引:0,他引:26
Microsatellite markers containing simple sequence repeats (SSR) are a valuable tool for genetic analysis. Our objective is to augment the existing RFLP map of rice with simple sequence length polymorphisms (SSLP). In this study, we describe 20 new microsatellite markers that have been assigned to positions along the rice chromosomes, characterized for their allelic diversity in cultivated and wild rice, and tested for amplification in distantly related species. Our results indicate that the genomic distribution of microsatellites in rice appears to be random, with no obvious bias for, or clustering in particular regions, that mapping results are identical in intersubspecific and interspecific populations, and that amplification in wild relatives ofOryza sativa is reliable in species most closely related to cultivated rice but becomes less successful as the genetic distance increases. Sequence analysis of SSLP alleles in three relatedindica varieties demonstrated the clustering of complex arrays of SSR motifs in a single 300-bp region with independent variation in each. Two microsatellite markers amplified multiple loci that were mapped onto independent rice chromosomes, suggesting the presence of duplicated regions within the rice genome. The availability of increasing numbers of mapped SSLP markers can be expected to increase the power and resolution of genome analysis in rice. 相似文献
85.
M. Sari-Gorla L. Rampoldi G. Binelli C. Frova M. E. Pè 《Molecular & general genetics : MGG》1996,251(5):551-555
Genetic factors controlling tolerance to the herbicide Alachlor in maize were localised by means of two different strategies. In the first approach, backcross (BC) plants, derived from pollen which had been subjected to selective pressure for resistance to the herbicide, were analysed for segregation distortion at 47 RFLP loci and compared to BC plants obtained from non-selected pollen. Preferential transmission of five chromosomal regions where putative QTLs (Quantitative Trait Loci) are localised was revealed in the BC plants from selected pollen. A second approach was based on a classical linkage analysis for segregation of the same set of RFLPs and factors controlling the trait, in a BC population of 210 individuals, by means of regression analysis. This study detected seven significant loci in four genomic regions. Overall, two loci revealed both segregation distortion and association with the expression of the trait, indicating linkage to genes expressed in both gametophytic and sporophytic phase. Three chromosomal regions appeared to carry factors involved in plant tolerance to Alachlor which are not expressed in pollen. Conversely, three loci were linked to factors selectable in pollen, but did not reveal significant association with tolerance in the plant in the segregating populations. 相似文献
86.
Summary A simple method using microcentrifuge tubes for determining fresh and dry weights, and collecting cell-free supernatant from plant suspension cultures is described. This method offers improvements in accuracy, precision, and time efficiency over traditional filtration methods. Using 4-day-old Nicotinia tabacum cultures, the centrifuge method was shown to remove 25% more of the interstitial water from cell aggregates compared to a suction filtration method, with significantly less variation in fresh weight data. 相似文献
87.
V. Kothekar 《Journal of biosciences》1996,21(5):577-597
We present here results of molecular dynamics (MD) simulations on hydrated bilayers of 40 molecules of 1-2-dimyristoyl-sn-glycero-3-phosphatidyl
choline (DMPC) in liquid crystalline (Lα) phase using two different models (i) with same (A) conformation for all DMPC molecules,
(ii) with alternate rows having different (A and B reported in crystallographic studies on DMPC) conformations. The bilayers
were hydrated using 776 and 1064 water molecules. Simulations have been carried out at 310K with AMBER 4.0 program, using
united atom force field for 200 pico seconds (ps) after equilibration. During heating and equilibration constant pressure
temperature (PT) conditions were maintained while in simulation of equillibrated bilayers constant volume temperature (VT)
conditions were used. Subaveraged atomic coordinates were used to calculate geometric parameters of lipid molecules and lipid
water interaction. Our results show larger flexibility of polar head group and glycerol region in Lα phase compared to gel
or non-hydrated bilayers. Chain disorder was more towards end. Sn-2 chains were more disordered. Use of two types of starting
conformations increased disorder. Trans fraction of chain torsional angle was higher in non-hydrated bilayer. However it was
more disordered due to ‘swing’ movement of chains because of distortion in torsional angles α2 and 03 due to absence of water
molecules. Trans fraction of the chains, order parameter and water penetration showed general agreement with the available
experimental results. On the whole MD technique was found to be quite useful for depicting microscopic behaviour of liquid
crystalline system and correlating the same with macroscopic changes observed experimentally. 相似文献
88.
K. Mengel 《Plant and Soil》1996,178(1):83-93
The root development of barley seedlings grown for one week in an aerated nutrient solution was studied in the presence of dissolved organic matter from an aqueous chestnut leaf litter extract. In particular, the different effects of low and high molecular weight fractions (small molecules: molecular weight <1000; large molecules: >10,000) of the leaf litter extract were examined. In the presence of large molecules root growth was inhibited, an irregular root tip morphology was observed, and Ca and Mg concentrations in the shoots were lower than in control plants. These phytotoxic effects were not caused by the formation of an impermeable layer of large molecules on the root surfaces that lower accessibility for nutrient cations as inferred from voltammetric experiments. A germination assay using spruce seeds, however, indicated allelochemical effects of large molecules, which exhibit a higher aromaticity than the small molecules as indicated by spectroscopic characterisation. In the growth experiments with small molecules, no influence on the root development of barley was evident, but an increase of Ca and Mg in the shoots was detected. During these growth experiments, a large amount of the small molecules, mainly simple phenols and amino acids, disappeared from the nutrient solution. The loss of small molecules was most likely the effect of mineralisation.Abbreviations DOC
dissolved organic carbon
- DOM
dissolved organic matter
- LLE
leaf litter extract
- MW
molecular weight
- HMDE
hanging mercury drop electrode 相似文献
89.
Estimation of the position and effect of a lethal factor locus on a molecular marker linkage map 总被引:3,自引:0,他引:3
R. Cheng A. Saito Y. Takano Y. Ukai 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,93(4):494-502
In the mapping of DNA markers the distortion of segregation of marker genotypes is often observed, which may be caused by a lethal factor acting in filial generations derived from distant crosses. A method is presented for estimating the recombination values between a lethal factor locus and neighboring molecular markers, and the relative viability or fertilization ability of gametes or zygotes affected by the lethal factor in an F2 population using the maximum likelihood method and the expectation conditional maximization (ECM) algorithm. Three selection models of gamete or zygote were considered, and the most likely one was determined by goodness of fit of the observed frequency of the phenotypes to the expected ones under the models. The method was applied to segregation data of molecular markers of an F2 population consisting of 144 individuals derived from a cross between an Indica and a Japonica rice variety. The presence of a lethal factor locus (L) located on chromosome III that caused partial gametic selection in both the male and female sides was suggested. The locus L was tightly linked to RFLP marker number 23 of the RFLP linkage map of Saito et al. (1991a), and the fertilization chance of a male or female gamete possessing the lethal factor was, on average, 41.5% of that of the normal gamete. 相似文献
90.
L. Gianfranceschi B. Koller N. Seglias M. Kellerhals C. Gessler 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,93(1-2):199-204
Large-scale marker-assisted selection requires highly reproducible, consistent and simple markers. The use of genetic markers is important in woody plant breeding in general, and in apple in particular, because of the high level of heterozygosity present in Malus species. We present here the transformation of two RAPD markers, which we found previously to be linked to the major scab resistance gene Vf, into more reliable and reproducible markers that can be applied directly to apple breeding. We give an example of how the use of such markers can speed up selection for the introduction of scab resistance genes into the same plant, reducing labour and avoiding time-consuming test crosses. We discuss the nature and relationship of the scab resistance gene Vf to the one present in Nova Easygro, thought to be Vr. 相似文献