Eliminating the Need for User-Definition of Gap Penalties using Linear Programming

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Rahul Bishnoi

IIT Guwahati
"Eliminating the Need for User-Definition of Gap Penalties using Linear Programming"
In the widely renowned `Needleman-Wunsch’ algorithm for sequence alignment, an affine gap penalty system is used for penalizing the algorithm for the usage of gaps. There are two types of gaps used: opening gap penalty and extending gap penalty, where the former refers to the introduction of a gap and the latter to the extension of pre-existing gaps. The choice of determining the values of these gap penalties has to be predefined by the user. As a result, there may arise an inefficient sequence alignment solely due to the poor choice of opening and extending gap penalties. In this poster, we aim to address this concern by constructing a mathematical black-box model which is governed by a set of linear equations in the form of a modified scoring system for judging the quality of the alignment. We use three dynamic programming states (Identity, Similarity, and DP score) to determine the optimal alignment. While iterating through various values of the scoring parameters, the highest cumulative score determines an optimal alignment and the respective gap penalty. For distantly-related and average-related sequences, our algorithm shows a significant increase in terms of identity and similarity for all the cases as compared to EMBOSS-Needle. We eliminate the need for the user to choose the gap penalties based on mere intuition and judgement and provide an automated method of choosing the optimal values specifically for each set of sequences.
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