Figure 3

Lateral gene transfer and homologous recombination together can produce organisms effectively belonging to several species at once. The all-blue, all-gold and red/green circles represent genomes from three different bacterial groups that might be designated species. Each circle represents an individual genome. There is effectively no homologous recombination (arrows) between genomes or areas of different colors. LGT has, however, recently created a mosaic genome (center), with segments derived from blue, gold and red/green species (itself a mosaic). Homologous recombination can occur between a segment introduced by LGT and the corresponding region of the original donor strain. Coherence is maintained between the segments and the donor DNA, as in the biological species model. This cartoon is of course unrealistic in several respects: regions shared between species are more likely to be scattered as islands in the genome, and the number of species to which some part of any genome belongs could be much greater.