The 'Butterfly effect' in Cayley graphs, and its relevance for evolutionary genomics

Abstract

Suppose a finite set $X$ is repeatedly transformed by a sequence of permutations of a certain type acting on an initial element $x$ to produce a final state $y$. We investigate how 'different' the resulting state $y'$ to $y$ can be if a slight change is made to the sequence, either by deleting one permutation, or replacing it with another. Here the 'difference' between $y$ and $y'$ might be measured by the minimum number of permutations of the permitted type required to transform $y$ to $y'$, or by some other metric. We discuss this first in the general setting of sensitivity to perturbation of walks in Cayley graphs of groups with a specified set of generators. We then investigate some permutation groups and generators arising in computational genomics, and the statistical implications of the findings.