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  • 1
    ISSN: 1432-1432
    Keywords: CpG dinucleotides ; Evolution ; Repetitive sequences ; Reverse transcriptase ; S1Bn retroposons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The identification of a family of SINE retroposons dispersed in the genome of oilseed rape Brassica napus has provided the basis for an evolutionary analysis of retroposition in plants. The repetitive elements (called S1Bn) are 170 by long and occupy roughly 500 loci by haploid genome. They present characteristic features of SINE retroposons such as a 3′ terminal A-rich region, two conserved polymerase III motifs (box A and B), flanking direct repeats of variable sizes, and a primary and secondary sequence homology to several tRNA species. A consensus sequence was made from the alignment of 34 members of the family. The retroposon population was divided into five subfamilies based on several correlated sets of mutations from the consensus. These precise separations in subfamilies based on “diagnostic” mutations and the random distribution of mutations observed inside each subfamily are consistent with the master sequence model proposed for the dispersion of mammalian retroposons. An independent analysis of each subfamily provides strong evidence for the coexpression of at least three subfamily master sequences (SMS). In contrast to mammalian retroposition, diagnostic positions are not shared between SMS. We therefore propose that SMS were all derived from a general master sequence (GMS) and independently activated for retroposition after a variable period of random drift. Possible models for plant retroposition are discussed.
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  • 2
    ISSN: 0168-9452
    Keywords: Triticum x Zea ; differentiation ; embryo culture ; morphogenesis ; ovule culture
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Icarus 89 (1991), S. 377-383 
    ISSN: 0019-1035
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2242
    Keywords: Polymorphism ; Restriction endonuclease ; Mapping ; Lettuce ; Lactuca sativa ; Resistance gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary As a first step in developing a detailed genetic map of lettuce (Lactuca sativa L.), 156 cDNA and 123 genomic DNA clones of lettuce were compared for their efficiency to detect restriction fragment length polymorphism (RFLP) between four lines of lettuce. Polymorphism was detected 2.5 times more frequently with cDNA probes than random genomic probes. Less polymorphism was detected with cDNA clones homologous to single copy than with cDNA clones homologous to multiple copy DNA sequences. A lower percentage of polymorphism was detected with genomic DNA clones homologous to repetitive sequences than with other types of probes. Digests with each of nine restriction endonucleases were compared; increased polymorphism was not correlated with the presence of a CpG dimer in the recognition sequence of the restriction endonuclease. Digests with enzymes recognizing four base pairs, however, displayed RFLPs less frequently. The six pairwise comparisons of the four lettuce lines showed different frequencies of polymorphism which only approximately corresponded to genetic distances obtained from previous isozyme analyses.
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  • 5
    ISSN: 1432-2242
    Keywords: Brassica napus ; Raphanus sativus ; Ogura cytoplasmic male-sterility restorer gene ; Bulked segregant analysis ; RAPD markers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Bulked segregant analysis was employed to identify random amplified polymorphic DNA (RAPD) markers linked to the restorer gene (Rfo) used in theOgura radish cytoplasmic male sterility of rapeseed. A total of 138 arbitrary 10-mer oligonucleotide primers were screened on the DNA of three pairs of bulks, each bulk corresponding to homozygous restored and male sterile plants of three segregating populations. Six primers produced repeatable polymorphisms between paired bulks. DNA from individual plants of each bulk was then used as a template for amplification with these six primers. DNA polymorphisms generated by four of these primers were found to be completely linked to the restorer gene with the polymorphic DNA fragments being associated either with the fertility restorer allele or with the sterility maintainer allele. Pairwise cross-hybridization demonstrated that the four polymorphic DNA fragments did not share any homology. Southern hybridization of labelled RAPD fragments on digested genomic DNA from the same three pairs of bulks revealed fragments specific to either the male sterile bulks or to the restored bulks and a few fragments common to all bulks, indicating that the amplified sequences are low copy. The four RAPD fragments that were completely linked to the restorer locus have been cloned and sequenced to develop sequence characterized amplified regions (SCARs). This will facilitate the construction of restorer lines used in breeding programs and is the first step towards map-based cloning of the fertility restorer allele.
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  • 6
    ISSN: 1432-2242
    Keywords: Key wordsBrassica napus ; L. Genetic mapping ; RFLP and RAPD markers ; Segregation distortions ; Comparative mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have undertaken the construction of a Brassica napus genetic map with isozyme (4%), RFLP (26.5%) and RAPD (68%) markers on a 152 lines of a doubled-haploid population. The map covers 1765 cM and comprises 254 markers including three PCR-specific markers and a morphological marker. They are assembled into 19 linkage groups, covering approximatively 71% of the rapeseed genome. Thirty five percent of the studied markers did not segregate according to the expected Mendelian ratio and tended to cluster in eight specific linkage groups. In this paper, the structure of the genetic map is described and the existence of non-Mendelian segregations in linkage analysis as well as the origins of the observed distortions, are discussed. The mapped RFLP loci corresponded to the cDNAs already used to construct B. napus maps. The first results of intraspecific comparative mapping are presented.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 94 (1997), S. 569-582 
    ISSN: 1432-2242
    Keywords: Key words Brassica napus ; Brassica oleracea ; Genetic maps ; RFLP ; RAPD
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The genus Brassica consists of several hundreds of diploid and amphidiploid species. Most of the diploid species have eight, nine or ten pairs of chromosomes, known respectively as the B, C, and A genomes. Genetic maps were constructed for both B. napus and B. oleracea using mostly RFLP and RAPD markers. For the B. napus linkage map, 274 RFLPs, 66 RAPDs, and two STS loci were arranged in 19 major linkage groups and ten smaller unassigned segments, covering a genetic distance of 2125 cM. A genetic map of B. oleracea was constructed using the same set of RFLP probes and RAPD primers. The B. oleracea map consisted of 270 RFLPs, 31 RAPDs, one STS, three SCARs, one phenotypic and four isozyme marker loci, arranged into nine major linkage groups and four smaller unassigned segments, covering a genetic distance of 1606 cM. Comparison of the B. napus and B. oleracea linkage maps showed that eight out of nine B. oleracea linkage groups were conserved in the B. napus map. There were also regions in the B. oleracea map showing homoeologies with more than one linkage group in the B. napus map. These results provided molecular evidence for B. oleracea, or a closely related 2n=18 Brassica species, as the C-genome progenitor, and also reflected on the homoeology between the A and C genomes in B. napus.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 94 (1997), S. 841-851 
    ISSN: 1432-2242
    Keywords: Key wordsBrassica juncea ; Mustard ; Linkage ; map ; RFLP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A genetic linkage map of Brassica juncea was constructed based on restriction fragment length polymorphism (RFLP) detected by anonymous cDNA markers from B. napus, using a segregating F1-derived doubled haploid (DH) progeny from a cross between a canola-quality mustard line (J90-4317) and a high-oil-content mustard line (J90-2733). The RFLP probes consisted of 229 cDNA probes from B. napus and a B. napus tandem repeat sequence, RDA2. The map consisted of 343 marker loci arranged in 18 major linkage groups plus five small segments with two to five marker loci, covering a total map distance of 2073 cM. Twenty-four percent of the markers were dominant in nature. Sixty-two percent of the marker loci were duplicated, and the majority were involved in inter-linkage group duplications, illustrating that complex duplications and subsequent rearrangements occurred after allopolyploidy. Deviation from the Mendelian segregation ratio for a DH population was observed for 27% of the markers. Two-thirds of these markers with a skewed segregation were clustered in 6 linkage groups and two unassigned segments. The overall average marker interval of the B. juncea map reported here was 6.6 cM, which would provide a marker density satisfactory for efficient use of the map in breeding applications, such as tagging of important agronomic traits and marker-assisted selection.
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  • 9
    ISSN: 1432-2242
    Keywords: Key words Self-incompatibility ; Brassica oleracea ; Brassica napus ; RFLP ; PCR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Self-incompatibility (SI) in Brassica is a sporophytic system, genetically determined by alleles at the S-locus, which prevents self-fertilization and encourages outbreeding. This system occurs naturally in diploid Brassica species but is introduced into amphidiploid Brassica species by interspecific breeding, so that in both cases there is a potential for yield increase due to heterosis and the combination of desirable characteristics from both parental lines. Using a polymerase chain reaction (PCR) based analysis specific for the alleles of the SLG (S-locus glycoprotein gene) located on the S-locus, we genetically mapped the S-locus of B. oleracea for SI using a F2 population from a cross between a rapid-cycling B. oleracea line (CrGC-85) and a cabbage line (86-16-5). The linkage map contained both RFLP (restriction fragment length polymorphism) and RAPD (random amplified polymorphic DNA) markers. Similarly, the S-loci were mapped in B. napus using two different crosses (91-SN-5263×87-DHS-002; 90-DHW-1855-4×87-DHS-002) where the common male parent was self-compatible, while the S-alleles introgressed in the two different SI female parents had not been characterized. The linkage group with the S-locus in B. oleracea showed remarkable homology to the corresponding linkage group in B. napus except that in the latter there was an additional locus present, which might have been introgressed from B. rapa. The S-allele in the rapid-cycling Brassica was identified as the S29 allele, the S-allele of the cabbage was the S 5 allele. These same alleles were present in our two B. napus SI lines, but there was evidence that it might not be the active or major SI allele that caused self-incompatibility in these two B. napus crosses.
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  • 10
    ISSN: 1432-2242
    Keywords: Microspore culture ; Responsiveness genes ; Comparative mapping ; Doubled haploid populations ; Brassica napus ; Segregation distortion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract RFLP segregation analyses were performed on a F2 population and two F1 microspore-derived populations from the same cross between a microspore culture-responsive parent (‘Topas’) and a non-responsive parent (‘Westar’). A total of 145 loci were detected with 87 cDNA clones. Eighty-two markers were common across all three populations. A total of 66 markers was assembled into 18 linkage groups and 16 markers remained unlinked. Segregation distortions were significant for 29% of the markers in the F2 population and 23% and 31% in microspore-derived populations M3 and M5, respectively. An equivalent number of markers showed biased segregation towards each parental allele in the F2 population while more markers showed a significant deviation from the expected Mendelian ratio towards the responsive parent in both microspore-derived populations. Different subsets of markers showed segregation distortions in the three populations indicating that the selective pressures leading to microsporederived plants are different from those acting during selfing of the F1. Linkage groups 1 and 18 were identified as putative chromosomal regions associated with microspore-culture responsiveness.
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