Conservation and divergence of repeated structures in Plasmodium genomes: the molecular drift

The rapid divergence of tandemly repeated families among Plasmodium species is in striking contrast with the extraordinary fidelity of the repeat copies present in a given genome. Close examination of the arrays of tandem repeats reveals an unsuspected regularity in the distribution of base substitutions, and clear relations between sets of repeats of different length, often coexisting in the same repeated region. The regular distribution of defects in the linear lattice gives rise to a hierarchy of periodicities. A model is proposed which accounts simultaneously for the rapid and concerted evolution of the repeats, and for the generation of supra-periodicities. The implications of this model with respect to repeated-pattern evolution are discussed.