For simplicity, we assume that back mutations occur at the same rate.

A number of restrictions governed whether back mutation took place:

Note that the remaining Old English diphthongs were due to other processes, such as breaking, back mutation and i-mutation.

If the sequences are sufficiently long that any back mutations can be neglected, then genotype space can be visualized as a tree (Fig.

Statistically one can assign variance based on the problem of randomnicity, back mutations, and parallel mutations (homoplasies) in creating an error range.

A back mutation or reversion is a point mutation that restores the original sequence and hence the original phenotype.

(It is safe to make this assumption, because the rate of back mutations from deleterious to advantageous mutants tends to have little effect on mutation-selection balance.)

Both methods M1 and M2 are based on the assumption that the fitness landscape can be represented as a tree, and that back mutations can be neglected.

As time since the divergence of two taxa increase, so does the probability of multiple substitutions on the same site, or back mutations, all of which result in homoplasies.

Daughter cells that inherit these wrong bases carry mutations from which the original DNA sequence is unrecoverable (except in the rare case of a back mutation, for example, through gene conversion).

Between pairs of taxa, some character changes that took place in ancestral lineages will be undetectable, because later changes have erased the evidence (often called multiple hits and back mutations in sequence data).

Asexual reproduction compels genomes to be inherited as indivisible blocks so that once the least mutated genomes in an asexual population begin to carry at least one deleterious mutation, no genomes with fewer such mutations can be expected to be found in future generations (except as a result of back mutation).