FACILITATED ISOLATION OF RARE RECOMBINANTS BY LIGASE CHAIN-REACTION -SELECTION FOR INTRAGENIC CROSSOVER EVENTS IN THE DROSOPHILA OPTOMOTORBLIND GENE

Ligase chain reaction (LCR) was evaluated as a tool for the detection of point mutations. For the mutation studied, the specificity of the m ethod is sufficient to detect the mutant allele in the presence of a 2 00-fold molar excess of the wild-type sequence. LCR was therefore empl oyed in a genetic recombination experiment as a probe for a recessive lethal point mutation. LCR greatly facilitated the isolation of a rare recombinant originating from a crossover event in the 40 kb interval separating the lethal mutation and an enhancer trap insertion in the o ptomotor-blind locus. The recombinant will allow the study of gene con trol in situ, in a largely unperturbed regulatory environment.