COMPARISON OF WHEAT PHYSICAL MAPS WITH BARLEY LINKAGE MAPS FOR GROUP-7 CHROMOSOMES

Comparative genetic maps among the Triticeae or Gramineae provide the possibility for combining the genetics, mapping information and molecu lar-marker resources between different species. Dense genetic linkage maps of wheat and barley, which have a common array of molecular marke rs, along with deletion-based chromosome maps of Triticum aestivum L. will facilitate the construction of an integrated molecular marker-bas ed map for the Triticeae. A set of 21 cDNA and genomic DNA clones, whi ch had previously been used to map barley chromosome 1 (7H), were used to physically map wheat chromosomes 7A, 7B and 7D. A comparative map was constructed to estimate the degree of linkage conservation and syn teny of chromosome segments between the group 7 chromosomes of the two species. The results reveal extensive homoeologies between these chro mosomes, and the first evidence for an interstitial inversion on the s hort arm of a barley chromosome compared to the wheat homoeologue has been obtained. In a cytogenetically-based physical map of group 7 chro mosomes that contain restriction-fragment-length polymorphic DNA (RFLP ) and random amplified polymorphic DNA (RAPD) markers, the marker dens ity in the most distal third of the chromosome arms was two-times high er than in the proximal region. The recombination rate in the distal t hird of each arm appears to be 8-15 times greater than in the proximal third of each arm where recombination of wheat chromosomes is suppres sed.