Fig. 1.

Methods using homologous recombination for gene deletions, with details for each method described in the text. a Basic homologous recombination using a non-replicating plasmid where 50% of colonies will be the desired deletion. b Homologous recombination using the positive selectable marker between the homology arms, flanked with recombination sites, and c homologous recombination using a replicating vector and three homology regions. Orange, homology regions, with “up” representing the DNA region upstream of the target gene, and “down” representing the DNA region downstream of the target gene; blue, target gene for deletion; green, counter-selectable markers; gray, positive selectable marker; crossed lines, sites of recombination