Simultaneous identification of duplications and lateral transfers

摘要

This paper introduces a combinatorial model that incorporates duplication events as well as lateral gene transfer events (a.k.a. horizontal gene transfer events). To the best of our knowledge, this is the first such model containing both of these events. A so-called dt-scenario is used to explain differences between a gene tree T and species trees S. The model is biologically as well as mathematically sound. Among other biological considerations, the model respects the partial order of evolution implied by S by demanding that the dt-scenarios are "acyclic". We present fixed parameter tractable algorithms that count the minimum number of duplications and lateral transfers, and more generally can compute the set of pairs (t,d) where d is the minimum number of duplications required by any explanation that requires t lateral transfers. This allows us to also compute a weighted parsimony score. We also show how gene loss events can be incorporated into our model. We also give an $NP$-completeness proof which suggests that the intractability is due to the demand that the dt-scenarios be acyclic. When this condition is removed, we can show that the problem is computable in polynomial time via dynamic programming. By generating "synthetic" gene and species trees via a birth-death process, we explored the capacity of our algorithms to faithfully reconstruct the actual number of events taken place. The results are positive.