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Patterns of genome duplication within the Brassica napus genome

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The progenitor diploid genomes (A and C) of the amphidiploid Brassica napus are extensively duplicated with 73% of genomic clones detecting two or more duplicate sequences within each of the diploid genomes. This comprehensive duplication of loci is to be expected in a species that has evolved through a polyploid ancestor. The majority of the duplicate loci within each of the diploid genomes were found in distinct linkage groups as collinear blocks of linked loci, some of which had undergone a variety of rearrangements subsequent to duplication, including inversions and translocations. A number of identical rearrangements were observed in the two diploid genomes, suggesting they had occurred before the divergence of the two species. A number of linkage groups displayed an organization consistent with centric fusion and (or) fission, suggesting this mechanism may have played a role in the evolution of Brassica genomes. For almost every genetically mapped locus detected in the A genome a homologous locus was found in the C genome; the collinear arrangement of these homologous markers allowed the primary regions of homoeology between the two genomes to be identified. At least 16 gross chromosomal rearrangements differentiated the two diploid genomes during their divergence from a common ancestor.Key words: genome evolution, Brassicaeae, polyploidy, homoeologous linkage groups.

Les génomes diploïdes ancestraux (A et C) de l'amphidiploïde Brassica napus sont fortement dupliqués puisque 73 % des clones génomiques détectent deux séquences ou plus au sein de chacun des génomes diploïdes. Cette duplication exhaustive des locus est attendue chez une espèce qui a évolué via un ancêtre polyploïde. La plupart des locus dupliqués au sein de chacun des génomes diploïdes étaient situés sur des groupes de liaison différents ou sous forme de segments colinéaires de locus liés dont certains avaient subi divers réarrangements suite à la duplication, tels que des inversions et des translocations. Plusieurs réarrangements identiques ont été observés chez les deux génomes, ce qui suggère que ceux-ci étaient survenus avant la divergence des deux espèces. Plusieurs groupes de liaison montraient une structure suggérant des événements de fusion/fission centrique, une observation qui porte à penser que ce mécanisme aurait joué un rôle dans l'évolution des génomes au sein du genre Brassica. Pour presque tous les locus situés sur le génome A, un locus homologue a été trouvé sur le génome C et la colinéarité de ces marqueurs homéologues a permis d'identifier les régions primaires d'homéologie entre ces deux génomes. Au moins 16 réarrangements chromosomiques d'importance ont contribué à différencier les deux génomes diploïdes au cours de leur divergence à partir d'un ancêtre commun.Mots clés : évolution génomique, brassicacées, polyploïdie, groupes de liaison homéologues.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2003-04-01

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  • From its inception in 1957, this international cytogenetics journal has catered to the research areas of the members of the Genetics Society of Canada; traditionally, these have included agriculture, entomology, genetics/cytogenetics, and evolutionary mechanisms. The contents of the journal have evolved as contributors developed new technologies and interests. A 20-member Editorial Board is composed of scientists from around the world. Reviews and commentary from respected experts are often featured.
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