DNA fingerprinting in sugar beet (Beta vulgaris) — identification of double-haploid breeding lines

Summary The distribution and abundance of simple repetitive sequences complementary to the synthetic oligonucleotides (GACA)₄, (GATA)₄, (GTG)₅ and (CA)₈ in the genomes of several cultivars of Beta vulgaris and in the wild beet B. vulgaris ssp. maritima were investigated. Hybridization experiments revealed that all four motifs were present, though at different abundances, in the genomes of all of the investigated beet cultivars. Considerable intraspecific variation of the resulting DNA fingerprints was observed. The extent of polymorphism depends on the oligonucleotide probe. The most informative banding patterns were obtained with the (GATA)₄ probe hybridized to HinfI-, HaeIII-, or RsaI-restricted DNA, respectively. DNA fingerprinting with (GATA)₄ allowed a clear differentiation of double-haploid breeding lines (DH lines). We demonstrated that the application of oligonucleotide probes for DNA fingerprinting is a sensitive tool for genome diagnosis in cultivated beet.     

Analysis of genetic variation in unisexual and bisexual lizard species of the genus Leiolepis from Southeast Asia

Using multilocus DNA fingerprinting with microsatellite probes (CAC)5, (GACA)4, (GGCA)4 and (GATA)4, intraspecific variation of the Southeast Asian lizards belonging to the genus Leiolepis (bisexual species Leiolepis reevesii and triploid parthenogenetic species Leiolepis guentherpetersi) was first examined. The L. guentherpetersi lizards were characterized by monophyletic DNA fingerprint profiles for the loci detected by the (GACA)4, (GGCA)4, and (CAC)5 probes, in terms of intrapopulation similarity index constituting S = 0.96. This was different from the individual-specific profiles of the lizards from bisexual, presumably parental species, L. reevesii (S = 0.6; P < 0.001). Genetic homogeneity of triploid L. guentherpetersi lizards at the loci examined serves as one of the arguments for the parthenogenetic nature of this species. Genetic variability of triploid parthenogenetic species L. guentherpetersi appeared to be comparable with that reported earlier for the Caucasian rock lizards of the genus Darevskia, namely, D. dahlia, D. armeniaca, and D. unisexualis (P > 0.05). The results of DNA fingerprinting analysis of the same L. guentherpetersi samples with the (GATA)4 hybridization probe were unexpected. Variability of parthenogenetic species L. guentherpetersi at the (GATA)n markers was remarkably higher than that at other DNA markers (S = 0.35; P = 3.08 x 10(-11)), being comparable to the variation of the (GATA)n DNA markers in bisexual species L. reevesii (P = 0.74). The reasons for high polymorphism of the (GATA)n-containing loci in L. guentherpetersi still remain unclear. This polymorhism is probably associated with high instability of the loci, which can be revealed by means of family analysis of parthenogenetic offspring.     

Abundance and polymorphism of simple repetitive DNA sequences in Bmssica napus L.

Summary The Brassica napus genome has been investigated by DNA fingerprinting with six synthetic oligonucleotide probes complementary to simple repetitive sequences, namely (GATA)₄, (GACA)₄, (GGAT)₄, (CA)₈, (CT)₈ and (GTG)₅. While all sequence motifs were found to be present in the B. napus genome, their organization and abundance varied considerably. Among the investigated probes, (GATA)₄ revealed the highest level of intraspecific polymorphism and distinguishes not only between cultivars but even between different individuals belonging to the same cultivar. In contrast, (GTG)₅, (GACA)₄ and (GGAT)₄ produced relatively homogeneous fingerprint patterns throughout different cultivars, while hybridization to (CT)₈ and (CA)₈ resulted in only a few weak bands superimposed on a smear. The isoschizomeric pair Hpa II and Msp I revealed the presence of methylated cytosines in the vicinity of (GATA)_m repeats. The applicability of simple repetitive sequence polymorphisms as molecular markers for Brassica species is discussed.     

Analysis of genetic variation in unisexual and bisexual lizard species of the genus Leiolepis from Southeast Asia

Using multilocus DNA fingerprinting with microsatellite probes (CAC)₅, (GACA)₄, (GGCA)₄, and (GATA)₄, intraspecific variation of the Southeast Asian lizards belonging to the genus Leiolepis (bisexual species Leiolepis reevesii and triploid parthenogenetic species Leiolepis guentherpetersi) was first examined. The L. guentherpetersi lizards were characterized by monophyletic DNA fingerprint profiles for the loci detected by the (GACA)₄, (GGCA)₄, and (CAC)₅ probes, in terms of intrapopulation similarity index constituting S = 0.96. This was different from the individual-specific profiles of the lizards from bisexual, presumably parental species, L. reevesii (S = 0.6; P < 0.001). Genetic homogeneity of triploid L. guentherpetersi lizards at the loci examined serves as one of the arguments for the parthenogenetic nature of this species. Genetic variability of triploid parthenogenetic species L. guentherpetersi appeared to be comparable with that reported earlier for the Caucasian rock lizards of the genus Darevskia, namely, D. dahli, D. armeniaca, and D. unisexualis (P > 0.05). The results of DNA fingerprinting analysis of the same L. guentherpetersi samples with the (GATA)₄ hybridization probe were unexpected. Variability of parthenogenetic species L. guentherpetersi at the (GATA)_n markers was remarkably higher than that at other DNA markers (S = 0.35; P = 3.08 × 10^?11), being comparable to the variation of the (GATA)_n DNA markers in bisexual species L. reevesii (P = 0.74). The reasons for high polymorphism of the (GATA)_n-containing loci in L. guentherpetersi still remain unclear. This polymorhism is probably associated with high instability of the loci, which can be revealed by means of family analysis of parthenogenetic offspring.     

Genetic diversity and phylogenetic relationships in Vigna Savi germplasm revealed by DNA amplification fingerprinting.

The pantropical genus Vigna (Leguminosae) comprises 7 cultivated species that are adapted to a wide range of extreme agroclimatic conditions. Few data are available on the relationships among these cultivated species or on their importance as sources of resistance against biotic and abiotic stresses. Therefore, we optimized DNA amplification fingerprinting (DAF) to estimate the genetic diversity within, and genetic relationships among, a representative core collection of cowpea, as compared with 16 accessions representing cultivars from 6 Vigna species. A set of 26 primers was selected from 262 tested random primers and used for the characterization of 85 Vigna accessions (6 V. angularis, 4 each of V. mungo and V. radiata, 2 V. umbellata, 1 V. aconitifolia, and 68 V. unguiculata), with Phaseolus vulgaris subsp. vulgaris as outgroup. A total of 212 polymorphic bands were used for maximum parsimony analysis. Our results clearly distinguished Brazilian from African V. unguiculata genotypes. At the species level, V. angularis was the most related and V. radiata the most divergent species relative to V. unguiculata. DAF markers were also informative at the intraspecific level, detecting a large diversity between cowpea cultivars. The implications of the presented results for cowpea breeding programs are discussed.     

Molecular cloning and analysis of one member of a polymorphic family of GACA-hybridising DNA repeats in tomato

Simple sequence repeat oligonucleotides were used to probe the tomato genome for elements displaying variability amongst commercial cultivars. The oligonucleotide (GACA)₄ was found to be particularly informative on genotype screening blots, hybridising to a highly polymorphic family of elements, and was used to clone one such member from a lambda library. The GACA-hybridisation was localised to a 1.3-kbHinfI fragment within the original 15-kb lambda insert. This 1,349-bp subclone (pT-GACA-2:1.3) was used to probe 27 Californian processing varieties and found to be capable of distinguishing all from each other, thus demonstrating its utility as a genetic fingerprinting probe for cultivar identification. Hybridisation occurred to approximately 10 major high molecular weight (> 4-kb) bands, most of which segregated independently in F₂ populations, as well as a large number of less clearly resolvable smaller fragments. Sequence analysis of the cloned element reveals that it is almost entirely composed of GACA or GATA repeats. These tetranucleotides are organised into distinct repetitive domains, consisting either of tandem arrays of each tetranucleotide or interspersions of GACA and GATA to form dodecanucleotides that are then further repeated. The boundaries between domains contain sufficient departures from the concensus repeat to allow construction of unique polymerase chain reaction (PCR) primers. Amplification from two such contiguous regions identifies length variation in both, thus yielding a genotype screen appropriate for high-throughput applications, such as assessment of purity in F₁ hybrid seed lots.     

Genomic variation in parthenogenetic lizard Darevskia armeniaca: evidence from DNA fingerprinting data

Microsatellites, or short tandem repeats, are abundant across genomes of most organisms. It is evident that the most straightforward and conclusive way of studying mutations in microsatellite-containing loci is to use clonally transmitted genomes or DNA sequences inherited in multigeneration pedigrees. At present, little is known about the origin of genetic variation in species that lack effective genetic recombination. DNA fingerprinting in 43 families of the parthenogenetic lizard species Darevskia armeniaca (131 siblings), using (GACA)(4), (GGCA)(4), (GATA)(4), and (CAC)(5) probes, revealed mutant fingerprints in siblings that differed from their mothers in several restriction DNA fragments. In some cases, the mutant fingerprints detected in siblings were also found in population samples. The mutation rate for new restriction fragment length estimated by using multilocus probes varied from 0.8 x 10(-2) to 4.9 x 10(-2) per band/per sibling. Probably, the most variations detected as restriction fragment length polymorphism have germ-line origin, but somatic changes of (CAC)(n) fingerprints in adult lizards were also observed. These results provide new evidence of existing unstable regions in genomes of parthenogenetic vertebrate animals, which provide genetic variation in unisexual populations.     

Early stages of sex chromosome differentiation in fish as analysed by simple repetitive DNA sequences

Animal sex chromosome evolution has started on different occasions with a homologous pair of autosomes leading to morphologically differentiated gonosomes. In contrast to other vertebrate classes, among fishes cytologically demonstrable sex chromosomes are rare. In reptiles, certain motifs of simple tandemly repeated DNA sequences like (gata)_n/(gaca)_m are associated with the constitutive heterochromatin of sex chromosomes. In this study a panel of simple repetitive sequence probes was hybridized to restriction enzyme digested genomic DNA of poeciliid fishes. Apparent male heterogamety previously established by genetic experiments in Poecilia reticulata (guppy) was correlated with male-specific hybridization using the (GACA)₄ probe. The (GATA)₄ oligonucleotide identifies certain male guppies by a Y chromosomal polymorphism in the outbred population. In contrast none of the genetically defined heterogametic situations in Xiphophorus could be verified consistently using the collection of simple repetitive sequence probes. Only individuals from particular populations produced sex-specific patterns of hybridization with (GATA)₄. Additional poeciliid species (P. sphenops, P. velifera) harbour different sex-specifically organized simple repeat motifs. The observed sex-specific hybridization patterns were substantiated by banding analyses of the karyotypes and by in situ hybridization using the (GACA)₄ probe.by E.R. SchmidtDedicated to Professor Karl Sperling on the occasion of his 50th birthday     

DNA fingerprinting in rice using oligonucleotide probes specific for simple repetitive DNA sequences

In this report we describe the use of five oligonucleotide probes, namely (GATA)₄, (GACA)₄, (GGAT)₄, (GAA)₆ and (CAC)₅, to reveal highly polymorphic DNA regions in rice. With each of the oligonucleotide probes, the level of polymorphism was high enough to distinguish several rice genotypes. Moreover, individual plants of one cultivar showed the same cultivar-specific DNA fingerprint. The multilocus fingerprint patterns were somatically stable. Our study demonstrates that microsatellite-derived DNA fingerprints are ideally suited for the identification of rice genotypes. As the majority of the probes detected a high level of polymorphism, they can be very useful in monitoring and aiding gene introgression from wild rice into cultivars.     

The organization of the evolutionarily conserved GATA/GACA repeats in the mouse genome

Simple repeated GATA and GACA sequences which were originally isolated from sex-specific snake satellite DNA have been found subsequently in all eukaryotes studied. The organization of these sequences within the mouse genome was investigated here by using synthetic oligonucleotide probes as a novel tool in comparison with conventional hybridization probes. Southern blot hybridization showed sex-specific patterns with both the (GATA)₄ and (GACA)₄ oligonucleotide probes, as previously described with conventional probes. The quantitative analysis of two mouse DNA phage libraries and of 25 isolated GATA-positive phage clones revealed intensive interspersion of GATA sequences with GACA, and with other repetitive and single-copy sequences. Ubiquitous interspersion and homogeneous genomic distribution of GATA and GACA sequences were confirmed by hybridization in situ of the oligonucleotide probes to metaphase chromosomes. The lengths of the GATA and GACA stretches were found to vary considerably in the individual phage clones. DNA inserts from 20 phages were assigned to autosomes and sex chromosomes and three genomic fragments were found to be confined to the Y chromosome. The organization of GATA and GACA sequences is discussed in the context of their evolutionary potential and possible conservation mechanisms.     

DNA fingerprinting in reptiles: Bkm hybridization patterns in Crocodilia and Chelonia

The simple tetranucleotide repeat GATA (GACA) occurs in all eukaryotes so far studied. In many species, the arrangement of these sequences varies considerably among individuals. Thus GATA (GACA) type probes produce DNA fingerprints when hybridized with restricted DNA from different individuals within a species. Banded krait minor (Bkm) satellite DNA (related to sequences originally recovered from the W chromosome of the banded krait and consisting essentially of a series of GATA repeats) is found in a wide spectrum of vertebrates and invertebrates. We used the Bkm 2(8) clone to evaluate the occurrence of this satellite in DNA from five species of Crocodilia and six species of Chelonia, including the sea turtles Chelonia mydas and Lepidochelys kempi. Well-resolved DNA fingerprints were obtained. Among the crocodilians, fewer restriction fragments were generated and fewer of the fragments were polymorphic, than among the chelonians, consistent with the view that the crocodilians are less divergent within species. The Bkm 2(8) clone can accordingly be used to advantage in individual, familial, and population studies, and perhaps in the evaluation of taxonomic relationships in these animals. This is of potential value in endangered species such as C. mydas and L. kempi.     

Nitrogen fixation and nodule occupancy by native strains of Rhizobium on different cultivars of common bean (Phaseolus vulgaris L.)

A field experiment under rainfed conditions was conducted in Durango, México, to assess N2-fixation of three cultivars of common bean (Phaseolus vulgaris L.) using ¹⁵N-methodology. In addition, diversity of rhizobial isolates obtained from nodules of the different plant genotypes was evaluated by intrinsic antibiotic resistance (IAR), PCR using enterobacterial repetitive intergenic consensus (ERIC) primers, PCR-RFLP analysis of the 16S rRNA gene and multilocus enzyme electrophoresis (MLEE). Selected isolates were used to determine acetylene reduction and competitive ability under greenhouse conditions. The three cultivars tested did not show high variation in N2-fixation, the %Ndfa values ranged from 19 to 26%. Variability in N2-fixation efficiency among various native rhizobial isolates was very high and our results indicate that differences in competitive abilitiy exist also. PCR-RFLP of the 16S rRNA gene and MLEE revealed that most of the isolates belong to the species Rhizobium etli. Intrinsic antibiotic resistance analysis and ERIC-PCR showed high diversity among isolates. In contrast, our results using MLEE show low genetic diversity (H = 0.105).     

Increased detectability of somatic changes in the DNA from human tumours after probing with “synthetic” and “genome-derived” hypervariable multilocus probes

Summary DNA fingerprinting with two minisatellite (33.15, M13) and two simple repeat probes [(GACA)₄, (CAC)₄/ (GTG)₅] was performed to screen for somatic changes in the DNA from various solid human tumours in comparison with constitutional DNA from the same patient. Loss of bands or changes in band intensitities were observed. Together the probes 33.15 and (CAC)₅/(GTG)₅ detected deviating fingerprint patterns in 63% of the colorectal carcinomas investigated. In mammary and stomach carcinomas, only 1/11 and 2/11 tumours, respectively, showed differences with either of the three probes, 33.15, (GACA)₄ and (CAC)₅/(GTG)₅.     

Contrasting rDNA evolution in lima bean (Phaseolus lunatus L.) and common bean (P. vulgaris L., Fabaceae)

Phaseolus vulgaris has two 5S rDNA sites in chromosomes 6 and 10 and from two up to nine 45S rDNA sites depending on the accession. The presence of three 45S rDNA sites, in chromosomes 6, 9 and 10, is considered the ancestral state for the species. For P. lunatus, only one 5S and one 45S rDNA sites in distinct chromosomes were known. In order to investigate the homeologies among these rDNA-bearing chromosomes and the stability of the rDNA sites in P. lunatus, rDNA and P. vulgaris chromosome-specific probes were hybridized in situ to P. lunatus. The chromosomes bearing the 5S and the 45S rDNA of P. lunatus are homeologous to chromosomes 10 and 6 of P. vulgaris, respectively. In contrast to the common bean, no variation in the number of rDNA loci was detected, except for a duplication of the 5S rDNA in the same chromosome in a small group of cultivars. These results suggest that the 5S rDNA site in chromosome 10 and the 45S rDNA site in chromosome 6 represent the ancestral loci in the genus. The 5S rDNA site in chromosome 10 of P. vulgaris is located in the long arm, while in P. lunatus it is present in the short arm, suggesting the occurrence of a transposition or a pericentric inversion after separation of both lineages.     

Variability of traits associated with phosphorus efficiency in wild and cultivated genotypes of common bean

Genetic variation in plant growth under limited phosphorus (P) supply is necessary to obtain more productive cultivars on low P-available soils. Two pot experiments were conducted to evaluate the variability of some traits associated with efficiency of P absorption and utilization in wild and cultivated genotypes of common bean (Phaseolus vulgaris L.) under biological N2 fixation. At two P levels (20 and 80 mg P kg-1 soil, P1 and P2, respectively), 20 wild and 6 cultivated genotypes were grown in Experiment 1, and 4 wild and 27 cultivated genotypes were grown in Experiment 2. Plants were harvested at flowering, but in Experiment 1 wild accessions that did not flower were harvested at the beginning of leaf senescence. In Experiment 1, part of the genotypic variability of wild accessions was attributed to a less homogeneous ontogenetic stage at harvest, whereas in Experiment 2 some variation in biomass production was due to distinct phenologies of cultivated genotypes. Wild lines did not seem more tolerant to low P conditions, but the genotypic variation observed suggests these materials as a source of genetic diversity. Part of the variation in the root area and root efficiency ratio (total P content:root area) was compensatory, resulting in narrow genotypic differences in the total P content. The total P content and root efficiency ratio presented a wider amplitude of variation at P2 than at P1, and P uptake was more influenced by P supply than root production. Since the genotype × P level interaction was not significant for shoot biomass and shoot P concentration in Experiment 2, P utilization efficiency may be a useful selection criterion for cultivars between limited and adequate P supply. Within the sample of genetic diversity evaluated herein, there was large genotypic variability for traits related to P efficiency among wild and cultivated genotypes of common bean.     

Light-dependent modulation of ribulose-1,5-bisphosphate carboxylase/oxygenase activity in the genus Phaseolus

Modulation of the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in low light and darkness was measured in A) 25 genotypes from the four cultivated species of Phaseolus (P. vulgaris, P. acutifolius, P. lunatus and P. coccineus), B) 8 non-cultivated Phaseolus species, and C) the related species Macroptileum atropurpureum. The activity ratio of Rubisco (the ratio of initial and total Rubisco activities, which reflects Rubisco carbamylation), and the molar activity of fully-activated Rubisco (which primarily reflects the inhibition of Rubisco activity by carboxyarabinitol 1-phosphate, CA1P) were assayed in leaves from the cultivated species sampled at midday in full sunlight, in low light at dusk (60 to 100 mol photons m^-2s^-1), and after at least 4 h in darkness. Dark inhibition of Rubisco molar activity was compared in both cultivated and non-cultivated species. In all cultivated genotypes, a significant reduction of the activity ratio of Rubisco was measured in leaves sampled at low light; however, the molar activity of fully activated Rubisco was not greatly reduced in these low light samples. In darkened leaves, molar activities substantially declined in most Phaseolus species with 11 of 13 exhibiting greater than 60% reduction. In P. vulgaris, the reduction of molar activity was extensive (greater than 69%) in all genotypes studied, which included wild progenitors as well as ancient and advanced cultivars. These results indicate that at low light late in the day, modulation of Rubisco activity is primarily through changes in carbamylation state, with CA1P playing a more limited role. By contrast in the dark, binding of CA1P dominates the modulation of Rubisco activity in Phaseolus in a pattern that appears to be conserved within a species, but can vary significantly between species within a genus. The degree of CA1P inhibition in Phaseolus was associated with phylogenetic affinities within the genus, as the species with extensive dark-inhibition of Rubisco activity tended to be more closely related to each other than to species with reduced inhibition of Rubisco activity.Abbreviations CA1P carboxyarabinitol 1-phosphate - CABP carboxyarabinitol bisphosphate - PFD photon flux density between 400 and 700 nm - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase     

Resistance of Phaseolus species to ice crystallization at subzero temperature

Dry bean ( Phaseolus vulgaris L.) cultivars possess little or no freezing tolerance and are killed at the temperature of ice formation in their tissues. An increase in frost tolerance by 2–3°C would expand dry bean production in the short growing seasons of the Canadian prairies and possibly to higher altitudes in the tropics where episodic frosts occur during the growing season. The objective of this study was to determine the differences in frost resistance of Phaseolus species in both controlled and field environments. Leaflets of dry bean cv. CDC Nighthawk, and wild relatives from the primary gene pool ( P. vulgaris var. mexicanus Freytag and P. vulgaris var. aborigineus (Burkart) Baudet) and the tertiary gene pool ( P. acutifolius var. tenuifolius A. Gray, P. filiformis Bentham, P. angustissimus A. Gray and P. ritensis M.E. Jones) were subjected to subzero temperatures with and without ice nucleation to determine the levels of tolerance and avoidance, respectively. The lethal temperature at which 50% of the leaflets were killed (LT₅₀) was 0.5–1°C lower for species of the tertiary gene pool compared to those from the primary gene pool. Leaflets of species from the tertiary gene pool were also characterized by extensive supercooling compared to leaflets of species from the primary gene pool. Resistance of Phaseolus species to spring and autumn frosts were determined on seedlings transplanted to the field. Phaseolus angustissimus , a species of the tertiary gene pool had the highest seedling survival in response to both autumn and spring frosts, when the minimum air temperatures were −5 and −7°C, respectively. Frost resistance of Phaseolus angustissimus , if successfully introgressed into bean germplasm, may enable the development of frost resistant dry bean cultivars.     

Instability of (GATA)<Subscript> n</Subscript> microsatellite loci in the parthenogenetic Caucasian rock lizard<Emphasis Type="Italic"> Darevskia unisexualis</Emphasis> (Lacertidae)

Mini- and microsatellites, comprising tandemly repeated short nucleotide sequences, are abundant dispersed repetitive elements that are ubiquitous in eukaryotic genomes. In humans and other bisexual species hypervariable mini- and microsatellite loci provide highly informative systems for monitoring of germline and somatic instability. However, little is known about the mechanisms by which these loci mutate in species that lack effective genetic recombination. Here, multilocus DNA fingerprinting was used to study M13 minisatellite and (GATA) _n microsatellite instability in the parthenogenetic Caucasian rock lizard Darevskia unisexualis (Lacertidae). DNA fingerprinting of 25 parthenogenetic families, from six isolated populations in Armenia (comprising a total of 84 siblings), using the oligonucleotide (GATA)₄ as a hybridization probe, revealed mutant fingerprinting phenotypes in 13 siblings that differed from their mothers in several restriction DNA fragments. In three families (8 siblings), the mutations were present in the germline. Moreover, the mutant fingerprint phenotypes detected in siblings were also present in population DNA samples. No intrafamily variations in DNA fingerprint patterns were observed with the M13 minisatellite probe. Estimates of the mutation rate for (GATA) _n microsatellite loci in D. unisexualis showed that it was as high as that seen in some bisexual species, reaching 15% per sibling or 0.95% per microsatellite band. Furthermore, in one case, a somatic (GATA) _n microsatellite mutation was observed in an adult lizard. These findings directly demonstrate that mutations in (GATA) _n microsatellite loci comprise an important source of genetic variation in parthenogenetic populations of D. unisexualis.Communicated by G. P. Georgiev     

The contribution of short repeats of low sequence complexity to large conifer genomes

The abundance and genomic organization of six simple sequence repeats, consisting of di-, tri-, and tetranucleotide sequence motifs, and a minisatellite repeat have been analyzed in different gymnosperms by Southern hybridization. Within the gymnosperm genomes investigated, the abundance and genomic organization of micro- and minisatellite repeats largely follows taxonomic groupings. We found that only particular simple sequence repeat motifs are amplified in gymnosperm genomes, while others such as (CAC)₅ and (GACA)₄ are present in only low copy numbers. The variation in abundance of simple sequence motifs reflects a similar situation to that found in angiosperms. Species of the two- and three-needle pine section Pinus are relatively conserved and can be distinguished from Pinus strobus which belongs to the five-needle pine section Strobus. The hybridization pattern of Picea species, bald cypress and gingko were different from the patterns detected in the Pinus species. Furthermore, sequences with homology to the plant telomeric repeat (TTTAGGG)_n have been analyzed in the same set of gymnosperms. Telomere-like repeats are highly amplified within two- and three- needle pine genomes, such as slash pine (Pinus elliottii Engelm. var. elliottii), compared to P. strobus, Picea species, bald cypress and gingko. P. elliottii var. elliottii was used as a representative species to investigate the chromosomal organization of telomere-like sequences by fluorescence in situ hybridization (FISH). The telomere-like sequences are not restricted to the ends of chromosomes; they form large intercalary and pericentric blocks showing that they are a repeated component of the slash pine genome.Conifers have genomes larger than 20000 Mbp, and our results clearly demonstrate that repeats of low sequence complexity, such to (CA)₈, (GA)₈, (GGAT)₄ and (GATA)₄, and minisatellite- and telomere-like sequences represent a large fraction of the repetitive DNA of these species. The striking differences in abundance and genome organization of the various repeat motifs suggest that these repetitive sequences evolved differently in the gymnosperm genomes investigated. Received: 1 October 1999 / Accepted: 3 November 1999