Plant Genome II Conference
Town & Country Conference Center, San Diego, CA, January, 1994.
PG-II: COLLINEARITY AND TRANSLOCATIONS IN THE DIPLOID BRASSICA SPECIES
AND GENOME INTERACTION IN AMPHIDIPLOID B. NAPUS
COLLINEARITY AND TRANSLOCATIONS IN THE DIPLOID BRASSICA SPECIES
AND GENOME INTERACTION IN AMPHIDIPLOID B. NAPUS.
Derek Lydiate, Andrew Sharpe, Isobel Parkin, Evelyne Bohuon and
Ulf Lagercrantz, Brassica & Oilseeds Research Department, John
Innes Centre, Norwich NR4 7UH, U.K.
Brassica napus is an amphidiploid which contains the genomes
of two diploid ancestors, B. rapa (the A genome) and B. oleracea
(the C genome). By comparing the RFLP map derived from a
conventional B. napus cross (c. 300 loci) with the map derived
from a cross between normal B. napus and a new interspecific (B.
rapa X B. oleracea) hybrid (c. 400 loci), we have demonstrated
that the A and C genomes of B. napus are essentially identical to
the current genomes of B. rapa and B. oleracea. The B. rapa and
B. oleracea chromosomes of resynthesised B. napus recognise
specific chromosomes in normal B. napus allowing us to identify
the ancestral origin of the 19 linkage groups of B. napus.
However, in the resynthesised B. napus, B. rapa chromosomes
frequently recombined with B. oleracea chromosomes (10% of all
recombination is homoeologous) demonstrating that established B.
napus lines have a system for controlling chromosome pairing.
The A and C genomes are extensively collinear, two pairs of
linkage groups are complete homoeologues and at least ten pairs
of half linkage groups are essentially unrearranged. Seven major
translocations explain most of the structural differences which
distinguish the genomes of B. rapa and B. oleracea. Our B.
oleracea RFLP map (c. 250 loci) is completely consistent with the
map of the C genome of B. napus, reinforcing the conclusion that
the two genomes are identical. Phylogenies based on nuclear and
organella RFLPs indicate that B. rapa and B. oleracea are very
closely related to each other but more distantly related to B.
nigra. However, our RFLP map of B. nigra (c. 300 loci) suggests
that its genome is extensively collinear with the genomes of B.
oleracea and B. rapa: at least ten pairs of half linkage groups
are essentially unrearranged between B. nigra and B. oleracea.
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