quasispecies

Quasispecies is a concept in molecular evolution and virology that describes a cloud of related genetic variants of a self-replicating molecule, typically an RNA genome, present in a population due to high mutation rates during replication. The population is centered around one or more master sequences with relatively high fitness, but continual mutation generates a spectrum of related genotypes. In this view, selection acts on the entire distribution in sequence space rather than on a single dominant genotype.

Origins and development: The quasispecies concept was introduced in the 1970s by Manfred Eigen and Peter Schuster, providing a mathematical framework for replication with error, and has become a fundamental model for understanding viral evolution, adaptation, and population diversity.

Key ideas: The genetic information of a quasispecies is distributed along a network of sequences connected by mutations. Although a master sequence may temporarily predominate, a mutational neighborhood maintains substantial genetic diversity. The theory also predicts an error threshold: if the mutation rate becomes too high, information cannot be maintained, risking an error catastrophe and loss of structure in the population.

Implications: Quasispecies dynamics enable rapid adaptation to changing environments, such as immune pressure or drug treatment, and can complicate efforts to control viral infections. They have been observed in many RNA viruses and other replicating systems, and influence strategies in vaccine design, antiviral development, and understanding evolutionary trajectories.

See also: error threshold, neutral networks, viral evolution, mutational robustness.