FIGURE 1: Genetic recombination and effective population sizes in symbiont/host and organelle/eukaryote populations. In symbiont/host populations, genetic recombination between individuals of the symbiont and host populations is independent. This allows for host populations to host more than one symbiont population (like symbiont populations B, C and D in host population F), for symbionts to recombine between individuals of different host populations (like symbiont population B which inhabits host populations E and F), and for individuals of different symbiont populations to inhabit the same host individuals. In organelle/eukaryote populations, genetic recombination between individuals of a population is coupled for the former partners, who now have identical effective population sizes; this also means that there is no distinction between individuals of the former host and the former symbiont.