Fig. 1.
Gene targeting in Drosophila. A, Ends-in technique and the elements of the donor construct. After transgenesis the combined action of FLP and endonuclease I-SceI generates the recombinogenic template, which produces the duplication at the target gene locus by homologous recombination. B, reduction of target gene repeats. The double-strand break caused by endonuclease I-CreI induces the second recombination. Ends-in targeting introduces a point mutation (green dot) in one of the alleles of the target gene. C, Ends-out technique. FLP and I-SceI generate a linear DNA molecule that undergoes homologous recombination with the target gene.