Mutational mechanisms and evolvability

Abstract

Well-studied cases of programmed DNA rearrangements, e.g., somatic recombination in the emergence of specific antibodies, suggest a rubric for specially evolved mutation systems: they amplify the rates of specific types of mutations (by orders of magnitude), subject to specific modulation, using dedicated parts, with the favored types of mutations being used repeatedly. Chapter 5 focuses on six types of systems that generate mutational diversity in a focused manner, often in an ecological context that makes sense of such a specialized feature, e.g., immune evasion or phage-host coevolution: cassette shuffling, phase variation (switching), CRISPR-Cas defenses, inversion shufflons, diversity-generating retro-elements, and mating-type switching. The emergence and influence of these systems relates to the concept of evolvability, here expressed in terms of three types of claims: evolvability as fact (E1), evolvability as explanans (E2), and evolvability as explanandum (E3).