Alternative mechanisms of concerted evolution. Both gene conversion and unequal crossover between duplicated sequences can homogenise duplicated sequences within a species (concerted evolution). This figure shows two interspersed duplicated sequences in direct orientation, which contain variant sites that distinguish the two sequences, shown as green and orange bars. Gene conversion homogenises these duplicates without any change in copy number of the duplicates in intermediate stages. Unequal crossovers can homogenise these repeats by repeated rounds of expansion and contraction with crossovers located at different locations within the duplicates. At each round, one of the two products of the previous unequal crossover (indicated by the double-headed arrow at the crossover point) undergoes an unequal crossover with the same repeat structure on the homologous chromosome.