Quasispecies

The above equations for the quasispecies then become for the discrete version: : or, for the continuum version: : Simple example The quasispecies concept can be illustrated by a simple system consisting of 4 sequences.

Assuming that the matrix W is a primitive matrix ( irreducible and aperiodic ), then after very many generations only the eigenvector with the largest eigenvalue will prevail, and it is this quasispecies that will eventually dominate.

Due to the ongoing production of mutant sequences, selection does not act on single sequences, but on mutational "clouds" of closely related sequences, referred to as quasispecies.

However, the quasispecies model does not predict the ultimate extinction of all but the fastest replicating sequence.

Mathematical description A simple mathematical model for a quasispecies is as follows: let there be possible sequences and let there be organisms with sequence i. Let's say that each of these organisms asexually gives rise to offspring.

Put simply, a quasispecies is a large group or cloud of related genotypes that exist in an environment of high mutation rate, where a large fraction of offspring are expected to contain one or more mutations relative to the parent.

The analog of fitness for a quasispecies is the tendency of nearby relatives within the cloud to be well-connected, meaning that more of the mutant descendants will be viable and give rise to further descendants within the cloud.

These subsets of sequences are the quasispecies.

When the fitness of a single genotype becomes meaningless because of the high rate of mutations, the cloud as a whole or quasispecies becomes the natural unit of selection.