Plant Genome II Conference
Town & Country Conference Center, San Diego, CA, January, 1994.
PG-II: HOMEOLOGOUS RECOMBINATION BETWEEN RFLP MARKERS IN WHEAT
CHROMOSOME 1A IN THE PRESENCE AND ABSENCE OF THE PH1 LOCUS
HOMEOLOGOUS RECOMBINATION BETWEEN RFLP MARKERS IN WHEAT
CHROMOSOME 1A IN THE PRESENCE AND ABSENCE OF THE PH1 LOCUS.
Jorge Dubcovsky & Jan Dvorak. Department of Agronomy & Range
Science, University of California, Davis, CA 95616, U.S.A.
Homoeologous recombination was studied between heat
chromosome 1A and chromosome IArec. which was substituted for
wheat (Triticum. aestivum) chromosome 1A in the presence and
absence of the wheat Ph1 locus. Chromosome 1Arec. had the entire
short arm and the proximal 50 cM of the long arm of T. monococcum
chromosome 1Am and distal 40 to 70 cM (cMWG710 to the telomere of
the long arm) of wheat chromosome 1A. Populations of recombinant
substitution lines (RSLs) from recombination between these two
chromosomes in the isogeneic background of Chinese Spring in the
presence and absence of the Ph1 locus were developed and were
used to produce RFLP maps. These maps were compared with a T.
monococcum 1A map and a wheat 1A map constructed in the isogenic
background of Chinese Spring wheat with the same RFLP markers.
In the absence of the Ph1 gene there was nearly homologous level
of recombination in the homoeologous portion of the two
chromosomes. However, when Ph1 was present, the length of the
homoeologous portion was reduced from 90 cM into 3 cM. The order
of loci appeared to be the same in chromosome 1Am of T.
monococcum and 1A of T. aestivum. The dramatic reduction in
recombination between the homoeologous chromatin in the presence
of the Ph1 gene was, therefore, caused by heterozygosity between
the homoeologous chromosomes. Recombination between homoeologous
chromosomes is suppressed by Phi by recognizing heterozygosity
along the entire chromosome rather than in specific regions, such
as telomeres or centromeres. This was indicated by the fact that
the distal homologous segment in the long arm of IArec. did not
bring about recombination in the neighboring homoeologous region.
Nor does Ph1 recognize the heterozygosity of only the centromere
region since chiasmata were formed in the distal homologous
segment, with a frequency comparable to that expected from
homologous recombination, in spite of that the centromeres of the
two chromosomes were homoeologous.
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