Figure 3.

How balancers work. Balancers both suppress recombination and prevent the recovery of crossover events that occur within an inversion. (A) A single crossover within a paracentric inversion (one that does not include the centromere) will result in an acentric fragment, which the cell discards, and a dicentric chromosome, which cannot segregate properly. (B) A single crossover within a paracentric inversion (one that encompasses the centromere) will produce chromosomes with large deletions and duplications, which are inviable to the cell. Balancers that incorporate more inversions are thus more effective [adapted from Miller et al. (2016b)].