Super short operations on both gene order and intergenic sizes
Résumé
Background: The evolutionary distance between two genomes can be estimated by computing a minimum length
sequence of operations, called genome rearrangements, that transform one genome into another. Usually, a genome
is modeled as an ordered sequence of genes, and most of the studies in the genome rearrangement literature consist
in shaping biological scenarios into mathematical models. For instance, allowing different genome rearrangements
operations at the same time, adding constraints to these rearrangements (e.g., each rearrangement can affect at most
a given number of genes), considering that a rearrangement implies a cost depending on its length rather than a unit
cost, etc. Most of the works, however, have overlooked some important features inside genomes, such as the pres-
ence of sequences of nucleotides between genes, called intergenic regions.
Results and conclusions: In this work, we investigate the problem of computing the distance between two
genomes, taking into account both gene order and intergenic sizes. The genome rearrangement operations we
consider here are constrained types of reversals and transpositions, called super short reversals (SSRs) and super short
transpositions (SSTs), which affect up to two (consecutive) genes. We denote by super short operations (SSOs) any SSR
or SST. We show 3-approximation algorithms when the orientation of the genes is not considered when we allow
SSRs, SSTs, or SSOs, and 5-approximation algorithms when considering the orientation for either SSRs or SSOs. We also
show that these algorithms improve their approximation factors when the input permutation has a higher number of
inversions, where the approximation factor decreases from 3 to either 2 or 1.5, and from 5 to either 3 or 2.
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