共查询到20条相似文献,搜索用时 15 毫秒
1.
Martin W. Ganal Nora L. V. Lapitan Steven D. Tanksley 《Molecular & general genetics : MGG》1988,213(2-3):262-268
Summary The major families of repeated DNA sequences in the genome of tomato (Lycopersicon esculentum) were isolated from a sheared DNA library. One thousand clones, representing one million base pairs, or 0.15% of the genome, were surveyed for repeated DNA sequences by hybridization to total nuclear DNA. Four major repeat classes were identified and characterized with respect to copy number, chromosomal localization by in situ hybridization, and evolution in the family Solanaceae. The most highly repeated sequence, with approximately 77000 copies, consists of a 162 bp tandemly repeated satellite DNA. This repeat is clustered at or near the telomeres of most chromosomes and also at the centromeres and interstitial sites of a few chromosomes. Another family of tandemly repeated sequences consists of the genes coding for the 45 S ribosomal RNA. The 9.1 kb repeating unit in L. esculentum was estimated to be present in approximately 2300 copies. The single locus, previously mapped using restriction fragment length polymorphisms, was shown by in situ hybridization as a very intense signal at the end of chromosome 2. The third family of repeated sequences was interspersed throughout nearly all chromosomes with an average of 133 kb between elements. The total copy number in the genome is approximately 4200. The fourth class consists of another interspersed repeat showing clustering at or near the centromeres in several chromosomes. This repeat had a copy number of approximately 2100. Sequences homologous to the 45 S ribosomal DNA showed cross-hybridization to DNA from all solanaceous species examined including potato, Datura, Petunia, tobacco and pepper. In contrast, with the exception of one class of interspersed repeats which is present in potato, all other repetitive sequences appear to be limited to the crossing-range of tomato. These results, along with those from a companion paper (Zamir and Tanksley 1988), indicate that tomato possesses few highly repetitive DNA sequences and those that do exist are evolving at a rate higher than most other genomic sequences. 相似文献
2.
Visualization of the terminal structure of rice chromosomes 6 and 12 with multicolor FISH to chromosomes and extended DNA fibers 总被引:12,自引:0,他引:12
High-resolution fluorescence in situ hybridization (FISH) on interphase and pachytene nuclei, and extended DNA fibers enabled microscopic distinction of DNA sequences less than a few thousands of base pairs apart. We applied this technique to reveal the molecular organization of telomere ends in japonica rice (Oryza sativa ssp. japonica), which consist of the Arabidopsis type TTTAGGG heptameric repeats and the rice specific subtelomeric tandem repeat sequence A (TrsA). Southern hybridizations of DNA digested with Bal31 and EcoRI, and FISH on chromosomes and extended DNA fibers demonstrated that (1) all chromosome ends possess the telomere tandem repeat measuring 3–4 kb; (2) the subtelomeric TrsA occurs only at the ends of the long arms of chromosomes 6 and 12, and measure 6 and 10 kb, which corresponds to 231 and 682 copies for these sites, respectively; (3) the telomere and TrsA repeats are separated by at most a few thousands of intervening nucleotide sequences. The molecular organization for a general telomere organization in plant chromosomes is discussed. 相似文献
3.
High-resolution physical mapping in Arabidopsis thaliana and tomato by fluorescence in situ hybridization to extended DNA fibres 总被引:6,自引:1,他引:5
Paul F. Fransz Carlos Alonso-Blanco Tsvetana B. Liharska Anton J.M. Peeters Pim Zabel J. Hans de Jong 《The Plant journal : for cell and molecular biology》1996,9(3):421-430
A technique to detect DNA sequences on extended DNA fibres (EDF) prepared from interphase nuclei from tomato (Lycopersicon esculentum) and Arabidopsis thaliana leaves by fluorescence in situ hybridization (FISH) is described. Three nuclear lysis procedures have been tested for their ability to decondense chromatin and to generate highly extended intact DNA fibres on microscopic slides. DNA probes of various sizes have been used in FISH experiments to EDFs to establish the resolution and sensitivity of the technique. The fluorescent signals of a 5S rDNA probe hybridized to tomato EDFs revealed continuous strings of about 200 µm, that corresponded to a molecular size of about 660 kb. In A. thaliana, a contig of three cosmids spanning a genomic region with a total length of about 89 kb was analysed. By means of multi-colour hybridization the physical positions of the cosmids were visualized as red and green fluorescence strings with overlapping regions in yellow. Comparison of the length of the fluorescent signals with the molecular data revealed a stretching degree of the DNA fibres at 3.27 kb µm?1, which is close to the Watson-Crick DNA length estimate of 2.9 kb µm?1. Other experiments on small size molecular probes with both lambda clones (13.5–17 kb insert sizes) and plasmids (4.2 and 5 kb) in a contig of A. thaliana, and the 5S rDNA region in tomato showed close agreement with molecular data. The lower limit of the detection, which was established in a hybridization experiment with two DNA probes from the 45S ribosomal gene on extended fibres of tomato, was about 0.7 kb. Consistent patterns of alternating fluorescent red and green spots were obtained reflecting the tandemly repeated arrangement of the 18S and 25S ribosomal sequences. On the basis of the microscopic distance between these hybridization spots the size of the ribosomal unit was estimated at 8.2 kb. This implies a drastic improvement of high-resolution physical mapping of DNA sequences by FISH on plant DNA. 相似文献
4.
Nigel L. Brown Tapan K. Misra Joseph N. Winnie Annette Schmidt Michael Seiff Simon Silver 《Molecular & general genetics : MGG》1986,202(1):143-151
Summary The DNA sequences of the mercuric resistance determinants of plasmid R100 and transposon Tn501 distal to the gene (merA) coding for mercuric reductase have been determined. These 1.4 kilobase (kb) regions show 79% identity in their nucleotide sequence and in both sequences two common potential coding sequences have been identified. In R100, the end of the homologous sequence is disrupted by an 11.2 kb segment of DNA which encodes the sulfonamide and streptomycin resistance determinants of Tn21. This insert contains terminal inverted repeat sequences and is flanked by a 5 base pair (bp) direct repeat. The first of the common potential coding sequences is likely to be that of the merD gene. Induction experiments and mercury volatilization studies demonstrate an enhancing but non-essential role for these merA-distal coding sequences in mercury resistance and volatilization. The potential coding sequences have predicted codon usages similar to those found in other Tn501 and R100 mer genes. 相似文献
5.
Fluorescence in situ hybridization (FISH) is a powerful approach for physical mapping of DNA sequences along plant chromosomes. Nematode-resistant sugar beets (Beta vulgaris) carrying aBeta procumbens translocation were investigated by FISH with two differentially labelled YACs originating from the translocation. At mitotic metaphases, the translocation was identified with both YACs in the terminal region on a pair of chromosomes. Meiotic chromosomes, representing a far more extended hybridization target, were used to determine the orientation of YACs with respect to chromosomal domains in combination with chromosomal landmark probes for telomeres and centromeres. The in situ detection of plant single-copy sequences is technically difficult, and the wild beet translocation was used to explore the potential resolution of the FISH approach and to introduce the chromosomal mapping of single-copy genes into genome analysis of Beta species. An internal fragment of the nematode resistance gene Hs1
pro–1, 684 bp long, was detected on both chromatids of different Beta chromosomes and represents one of the shortest unique DNA sequences localized on mitotic plant chromosomes so far. Comparative chromosomal mapping of the 684 bp Hs1
pro–1 probe in the translocation line, a monosomic addition line and in B. procumbens revealed the origin of the wild beet translocation leading to nematode-resistant sugar beets. 相似文献
6.
Richard Jorgensen Christine Snyder Jonathan D. G. Jones 《Molecular & general genetics : MGG》1987,207(2-3):471-477
Summary The detailed structural organization of DNA sequences transferred to the plant genome via Agrobacterium tumefaciens has been determined in 11 transgenic tomato plants that carry the transferred DNA (T-DNA) at a single genetic locus. The majority (seven) of these plants were found to carry multiple copies of T-DNA arranged in inverted repeat structures. Such a high frequency of inverted repeats among transgenotes has not been previously reported and appears to be characteristic of transformation events caused by C58/pGV3850 strains of Agrobacterium. The inverted repeats were found to be centered on either the left or the right T-DNA boundary and both types were observed at similar frequency. In several plants both types of inverted repeat were found to coexist in the same linear array of elements. Direct repeats were observed in two plants, each time at the end of an array of inverted repeat elements, and at a lower frequency than inverted repeats. The junctions between T-DNA elements and plant DNA sequences and the junctions between adjacent T-DNA elements were mapped in the same 11 plants, allowing the determination of the distribution of junction points at each end for both types of junction. Based on a total of 17 distinct junctions at the right end of T-DNA and 19 at the left end, the distribution of junction points was found to be much more homogeneous at the right end than at the left end. Left end junctions were found to be distributed over a 3 kb region of T-DNA with two thirds of the junctions within 217 bp of the left repeat. Two thirds of the right end junctions were found to lie within 11 bp of the right repeat with the rest more than 39 bp from the right repeat. T-DNA::plant DNA junctions and T-DNA::T-DNA inverted repeat junctions showed similar distributions of junction points at both right and left ends. The possibilities that T-DNA inverted repeats are unstable in plants and refractory to cloning in wild type Escherichia coli is discussed. Two distinct types of mechanisms for inverted repeat formation are contrasted, replication and ligation mechanisms. 相似文献
7.
Deborah S. Shumard Lawrence I. Grossman Michael E. S. Hudspeth 《Molecular & general genetics : MGG》1986,202(1):16-23
Summary Mitochondrial DNA from four strains of the oomycete Achlya has been compared and nine gene loci mapped, including that of the ribosomal protein gene, var1. Examination of the restriction enzyme site maps showed the presence of four insertions relative to a map common to all four strains. All the insertions were found in close proximity to genic regions. The four strains also cotained the inverted repeat first observed in A. ambisexualis (Hudspeth et al. 1983), allowing an examination by analysis of retained restriction sites of the evolutionary stability of repeated DNA sequences relative to single copy sequences. Although the inverted repeat is significantly more stable than single copy sequences, more detailed analysis indicated that this stability is limited to the portion encoding the ribosomal RNA genes. Thus, the apparent evolutionary stability of the repeat does not appear to derive from the inverted repeat structure per se.Abbreviations ATPase 6, 9
genes for ATPase subunits 6 and 9
- COI, II, III
genes for cytochrome oxidase subunits 1, 2, and 3
- COB
gene for apocytochrome b
- L-, S-RNA
genes for the mitochondrial large and small ribosomal RNAs
- mtDNA
mitochondrial DNA
-
var1
gene for the S. cerevisiae mitochondrially, encoded ribosomal protein
- m.u.
map units
- bp
base pairs
- kb
kilobase pairs 相似文献
8.
M. Ganal V. Hemleben 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,73(1):129-135
Summary The AT-rich highly repeated satellite DNA of Cucurbita pepo (zucchini) and Cucurbita maxima (pumpkin) were cloned and their DNA structure was investigated. DNA sequencing revealed that the repeat length of satellite DNA in Cucurbita pepo is 349–352 base pairs. The percentage of AT-base pairs is about 61%. This satellite is highly conserved in restriction enzyme pattern and DNA sequence; sequence heterogeneity is about 10%. In contrast, the satellite DNA of Cucurbita maxima has a repeat length of 168–169 base pairs. This satellite is also rich in AT-base pairs (64%), existing in at least three different variants as revealed by restriction enzyme analysis and DNA sequencing. The sequence heterogeneity between these variants is about 15%. The two satellite DNAs showed no cross-hybridization to each other and sequence homology is only limited. Nevertheless, we found in the C. pepo genome a high amount of sequences resembling the satellite of C. maxima. In contrast, the satellite repeat of C. pepo is found in the C. maxima DNA only in a few copies. These observations were discussed with respect to satellite DNA evolution and compared to the data received from monocotyledonous species. 相似文献
9.
Summary Fifty random clones (350–2300 bp), derived from sheared, nuclear DNA, were studied via Southern analysis in order to make deductions about the organization and evolution of the tomato genome. Thirty-four of the clones were mapped genetically and determined to represent points on 11 of the 12 tomato chromosomes. Under moderate stringency conditions (80% homology required) 44% of the clones were classified as single copy. Under higher stringency, the majority of the clones (78%) behaved as single copy. Most of the remaining clones belonged to multicopy families containing 2–20 copies, while a few contained moderately or highly repeated sequences (10% at moderate stringency, 4% at high stringency). Divergence rates of sequences homologous to the 50 random genomic clones were compared with those corresponding to 20 previously described cDNA (coding sequence) clones. Rates were measured by probing each clone (random genomics and cDNAs) onto filters containing DNA from various species from the family Solanaceae (including potato, Datura, petunia and tobacco) as well as one species (watermelon) from another plant family, Cucurbitaceae. Under moderate stringency conditions, the majority of the random clones (single copy and repetitive) failed to detect homologous sequences in the more distantly related species, whereas approximately 90% of the 20 coding sequences analyzed could still be detected in all solanaceous species. The most highly repeated sequences appear to be the fastest evolving and homologous copies could be detected only in species most closely related to tomato. Dispersion of repetitive sequences, as opposed to tandem clustering, appears to be the rule for the tomato genome. None of the repetitive sequences discovered by this random sampling of the genome were tandemly arranged — a finding consistent with the notion that the tomato genome contains only a small fraction of satellite DNA. This study, along with a companion paper (Ganal et al. 1988), provides the first general sketch of the tomato genome at the molecular level and indicates that it is comprised largely of single copy sequences and these sequences, together with repetitive sequences are evolving at a rate faster than the coding portion of the genome. The small genome and paucity of highly repetitive DNA are favourable attributes with respect to the possibilities of conducting chromosome walking experiments in tomato and the fact that coding regions are well conserved among solanaceous species may be useful for distinguishing clones that contain coding regions from those that do not. 相似文献
10.
Chromosome identification is essential in oyster genomic research. Fluorescence in situ hybridization (FISH) offers new opportunities for the identification of oyster chromosomes. It has been used to locate satellite DNAs, telomeres or ribosomal DNA sequences. However, regarding chromosome identification, no study has been conducted with simple sequence repeats (SSRs). FISH was used to probe the physical organization of three particular SSRs, (GGAT)(4), (GT)(7) and (TA)(10) onto metaphase chromosomes of the Pacific oyster, Crassostrea gigas. Hybridization signals were observed in all the SSR probes, but the distribution and intensity of signals varied according to the oligonucleotide repeat. The intercalary, centromeric and telomeric bands were observed along the chromosomes, and for each particular repeat every chromosome pair presented a similar pattern, allowing karyotypic analysis with all the SSRs tested. Our study is the first in mollusks to show the application of SSR in situ hybridization for chromosome identification and karyotyping. This technique can be a useful tool for oyster comparative studies and to understand genome organization in different oyster taxa. 相似文献
11.
Fluorescence in situ hybridisation (FISH) is a rapid and reliable technique for chromosomal investigations that is used for a wide variety of
cytogenetic purposes at present. This molecular-cytogenetic method has been developed continuously for many years. As a consequence,
various modifications with different kinds of fluorescently labelled probes have been introduced to optimise the detection
of DNA and RNA sequences. This review articlepaper presents the general principles of in situ hybridisation, probe labelling and examples of proper use of different kinds of probes. In addition, some newer FISH methods
and their usefulness in human molecular cytogenetics are described. 相似文献
12.
Direct isolation of cDNA sequences from specific chromosomal regions of the tomato genome by the differential display technique 总被引:2,自引:0,他引:2
The differential display technique was originally developed for the isolation of differentially expressed genes from eukaryotic tissues. We have adapted this technique for the isolation of cDNA markers from specific regions of the tomato genome. For this purpose, differential display was performed on RNA extracted from leaf tissue of nearly isogenic lines for the Tm-2a gene of tomato. On average, one out of 20 primer combinations resulted in a polymorphism at the cDNA level. When used as hybridization probes, all of these cDNA fragments were single or low copy and all of them were polymorphic on Southern hybridizations using DNA from the isogenic lines. Genetic mapping revealed in each case at least one locus in the introgressed segment on chromosome 9 of tomato. Thus, this technique might provide a way for the direct isolation of transcribed sequences from specific regions of any animal or plant genome for which such lines exist. 相似文献
13.
植物荧光原位杂交技术的发展及其在植物基因组分析中的应用 总被引:12,自引:0,他引:12
荧光原位杂交(FISH)是在染色体、间期核和DNA纤维上定位特定DNA序列的一种有效而精确的分子细胞遗传学方法。20年来,植物荧光原位杂交技术发展迅速:以增加检测的靶位数为目的,发展了双色FISH、多色FISH和多探针FISH鸡尾酒技术;为增加很小染色体目标的检测灵敏度,发展了BAC-FISH和酪胺信号放大FISH(TSA-FISH)等技术;以提高相邻杂交信号的空间分辨力为主要目的,发展了高分辨的粗线期染色体FISH、间期核FISH、DNA纤维FISH和超伸展的流式分拣植物染色体FISH技术。在植物基因组分析中,FISH技术发挥了不可替代的重要作用,它可用于:物理定位DNA序列,并为染色体的识别提供有效的标记;对相同DNA序列进行比较物理定位,探讨植物基因组的进化;构建植物基因组的物理图谱;揭示特定染色体区域的DNA分子组织;分析间期核中染色质的组织和细胞周期中染色体的动态变化;鉴定植物转基因。 相似文献
14.
M. R. Thomas S. Matsumoto P. Cain N. S. Scott 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1993,86(2-3):173-180
Summary Repetitive DNA sequences present in the grapevine genome were investigated as probes for distinguishing species and cultivars. Microsatellite sequences, minisatellite sequences, tandemly arrayed genes and highly repetitive grapevine sequences were studied. The relative abundance of microsatellite and minisatellite DNA in the genome varied with the repeat sequence and determined their usefulness in detecting RFLPs. Cloned Vitis ribosomal repeat units were characterised and showed length heterogeneity (9.14–12.15 kb) between and within species. A highly repetitive DNA sequence isolated from V. vinifera was found to be specific only to those species classified as Euvitis. DNA polymorphisms were found between Vitis species and between cultivars of V. vinifera with all classes of repeat DNA sequences studied. DNA sequences suitable for DNA fingerprinting gave genotype-specific patterns for all of the cultivars and species examined. The DNA polymorphisms detected indicates a moderate to high level of heterozygosity in grapevine cultivars.On leave from the Biochemical Research Institute, Nippon Menard Cosmetic Co, Ltd, Ogaki Gifuken, 503 Japan 相似文献
15.
Two molecular cytogenetics methods, PRINS (primed in situ DNA labeling) and C-PRINS (cycling PRINS), were optimized for the physical mapping of several types of DNA sequences on the
mitotic chromosomes of the narrow-leafed lupin (Lupinus angustifolius L.). The fragment of the FokI element from Vicia faba was localised by indirect PRINS reaction. Two other sequences, fragments of the coding sequences of L. luteus and of L. angustifolius, were localised by indirect C-PRINS. These techniques are faster and more sensitive than FISH, and they allowed the mapping
of short DNA fragments. The data obtained shows that both types of PRINS are valuable tools for chromosome identification
in lupin. 相似文献
16.
Construction of a yeast artificial chromosome library of tomato and identification of cloned segments linked to two disease resistance loci 总被引:18,自引:0,他引:18
Gregory B. Martin Martin W. Ganal Steven D. Tanksley 《Molecular & general genetics : MGG》1992,233(1-2):25-32
Summary We have constructed a yeast artificial chromosome (YAC) library of tomato for chromosome walking that contains the equivalent of three haploid genomes (22 000 clones). The source of high molecular weight DNA was leaf protoplasts from the tomato cultivars VFNT cherry and Rio Grande-PtoR, which together contain loci encoding resistance to six pathogens of tomato. Approximately 11 000 YACs have been screened with RFLP markers that cosegregate withTm-2a andPto — loci conferring resistance to tobacco mosaic virus andPseudomonas syringae pv.tomato, respectively. Five YACs were identified that hybridized to the markers and are therefore starting points for chromosome walks to these genes. A subset of the library was characterized for the presence of various repetitive sequences and YACs were identified that carried TGRI, a repeat clustered near the telomeres of most tomato chromosomes, TGRII, an interspersed repeat, and TGRIIl, a repeat that occurs primarily at centromeric sites. Evaluation of the library for organellar sequences revealed that approximately 10% of the clones contain chloroplast sequences. Many of these YAC clones appear to contain the entire 155 kb tomato chloroplast genome. The tomato cultivars used in the library construction, in addition to carrying various disease resistance genes, also contain the wild-type alleles corresponding to most recessive mutations that have been mapped by classical linkage analysis. Thus, in addition to its utility for physical mapping and genome studies, this library should be useful for chromosome walking to genes corresponding to virtually any phenotype that can be scored in a segregating population. 相似文献
17.
Jose M. Martinez-Zapater Mark A. Estelle Chris R. Somerville 《Molecular & general genetics : MGG》1986,204(3):417-423
Summary Three members of a family of highly repeated DNA sequences from Arabidopsis thaliana have been cloned and characterized. The repeat unit has an average length of 180 bp and is tandemly repeated in arrays longer than 50 kb. This family represents more than one percent of the Arabidopsis genome. Sequence comparisons with tandemly repeated DNA sequences from other Cruciferae species show several regions of homology and a similar length of the repeat unit. Homologies are also found to highly repeated sequences from other plant species. When the sequence CCGG occurs in the repeated DNA, the inner cytosine is generally methylated. 相似文献
18.
Complete sequence determination of the mitochondrial (mt) genome of the sea scallop Placopecten magellanicus reveals a molecule radically different from that of the standard metazoan. With a minimum length of 30,680 nucleotides (nt;
with one copy of a 1.4 kilobase (kb) repeat) and a maximum of 40,725 nt, it is the longest reported metazoan mitochondrial
DNA (mtDNA). More than 50% of the genome is noncoding (NC), consisting of dispersed, imperfectly repeated sequences that are
associated with tRNAs or tRNA-like structures. Although the genes for atp8 and two tRNAs were not discovered, the genome still has the potential for encoding 46 genes (the additional genes are all
tRNAs), 9 of which encode tRNAs for methionine. The coding portions appear to be evolving at a rate consistent with other
members of the pectinid clade. When the NC regions containing “dispersed repeat families” are examined in detail, we reach
the conclusion that transposition involving tRNAs or tRNA-like structures is occurring and is responsible for the large size
and abundance of noncoding DNA in the molecule. The rarity of enlarged mt genomes in the face of a demonstration that they
can exist suggests that a small, compact organization is an actively maintained feature of metazoan mtDNA.
Reviewing Editor: Gail Simmons 相似文献
19.
Hong-Bin Zhang Gregory B. Martin Steven D. Tanksley Rod A. Wing 《Molecular & general genetics : MGG》1994,244(6):613-621
A map-based cloning technique for crop plants is being developed using tomato as a model system. The target gene jointless is a recessive mutation that completely suppresses the formation of flower and fruit pedicel abscission zones. Previously, the jointless locus was mapped to a 3 cM interval between the two molecular markers TG523 and RPD158. Physical mapping of the jointless region by pulsed-field gel electrophoresis demonstrated that TG523 and RPD158 reside on a 600 kb SmaI fragment. In this study, TG523 was used as a probe to screen a tomato yeast artificial chromosome (YAC) library. Six tomato YAC (TY) clones were isolated, ranging from 220 to 380 kb in size. Genetic mapping of YAC ends demonstrated that this set of overlapping YACs encompasses the jointless locus. Two YAC ends, TY159L (L indicates left end) and TY143R (R indicates right end), cosegregate with the jointless locus. Only one of the six YACs (TY142) contained single-copy DNA sequences at both ends that could be mapped. The two ends of TY142 were mapped to either side of the jointless locus, indicating that TY142 contains a contiguous 285 kb tomato DNA fragment that probably includes the jointless locus. Physical mapping of the TY142 clone revealed that TY159L and TY143R reside on a 55 kb SalI fragment. Southern blot hybridization analysis of the DNAs of tomato lines nearly isogenic for the jointless mutation has allowed localization of the target locus to a region of less than 50 kb within the TY142 clone.Communicated by H. Saedler 相似文献
20.
A modified DNA microarray-based technique was devised for preliminary screening of short fragment genomic DNA libraries from three Vicia species (V. melanops, V. narbonensis, and V. sativa) to isolate representative highly abundant DNA sequences that show different distribution patterns among related legume species. The microarrays were sequentially hybridized with labeled genomic DNAs of thirteen Vicia and seven other Fabaceae species and scored for hybridization signals of individual clones. The clones were then assigned to one of the following groups characterized by hybridization to: (1) all tested species, (2) most of the Vicia and Pisum species, (3) only a few Vicia species, and (4) preferentially a single Vicia species. Several clones from each group, 65 in total, were sequenced. All Group I clones were identified as rDNA genes or fragments of chloroplast genome, whereas the majority of Group II clones showed significant homologies to retroelement sequences. Clones in Groups III and IV contained novel dispersed repeats with copy numbers 102–106/1C and two genus-specific tandem repeats. One of these belongs to the VicTR-B repeat family, and the other clone (S12) contains an amplified portion of the rDNA intergenic spacer. In situ hybridization using V. sativa metaphase chromosomes revealed the presence of the S12 sequences not only within rDNA genes, but also at several additional loci. The newly identified repeats, as well as the retroelement-like sequences, were characterized with respect to their abundance within individual genomes. Correlations between the repeat distributions and the current taxonomic classification of these species are discussed. 相似文献