Figure 7-4: Insertion and looping out of specialized transducing phage. The lambda gal+ can insert into the chromosome either by site-specific recombination at att or by homology-dependent recombination in host DNA between gal and attlambda. The product (a heterogenote) has two copies of gal, separated by lambda DNA. During growth of the strain, the lambda gal can occasionally loop out through homology-dependent recombination. Depending on the position of the crossover point, the haploid derivative can carry either the gal gene of the original chromosome or that brought in by the phage. Looping out to give the chromosomal gene happens at about 10-3 per generation. The rate for the phage-derived gene (in the case, gal+) is lower and depends on the extent of homology to the left of gal. The reciprocal product (an excised lambda gal, which, if formed, does not replicate and is therefore diluted out by growth) is not shown.