ANCHOR PROBES FOR COMPARATIVE MAPPING OF GRASS GENERA

Comparative mapping of cDNA clones provides an important foundation fo r examining structural conservation among the chromosomes of diverse g enera and for establishing hypotheses about the relationship between g ene structure and function in a wide range of organisms. In this study , ''anchor probes'' were selected from cDNA libraries developed from r ice, oat, and barley that were informative for comparative mapping in the grass family. One thousand eight hundred probes were screened on g arden blots containing DNA of rice, maize, sorghum, sugarcane, wheat, barley, and oat, and 152 of them were selected as ''anchors'' because (1) they hybridized to the majority of target grass species based on S outhern analysis, (2) they appeared to be low or single copy in rice, and (3) they helped provide reasonably good genome coverage in all spe cies. Probes were screened for polymorphism on mapping parents, and po lymorphic markers were mapped onto existing species-specific linkage m aps of rice, oat, maize, and wheat. In wheat, both polymorphic and mon omorphic markers could be assigned to chromosomes or chromosome arms b ased on hybridization to nullitetrasomic and ditelosomic stocks. Linka ge among anchored loci allowed the identification of homoeologous regi ons of these distantly related genomes. Anchor probes were sequenced f rom both ends, providing an average of 260 bp in each direction, and s equences were deposited in GenBank. BLAST was used to compare the sequ ences with each other and with a nonredundant protein sequence databas e maintained at the European Molecular Biology Laboratory (EMBL). Of t he anchor probes identified in this study 78% showed significant simil arity to protein sequences for known genes with BLASTX scores exceedin g 100.