Evolution of biological sequences implies an extreme value distribution of type I for both global and local pairwise alignment s

Background: Confidence in pairwise alignments of biological sequences, obtained by various methods such as Blast or Smith-Waterman, is critical for automatic analyses of genomic data. Two statistical models have been proposed. In the asymptotic limit of long sequences, the Karlin-Altschul model is based on the computation of a P-value, assuming that the number of high scoring matching regions above a threshold is Poisson distributed. Alternatively, the Lipman-Pearson model is based on the computation of a Z-value from a random score distribution obtained by a Monte-Carlo simulation. Z-values allow the deduction of an upper bound of the P-value (1/Z-value2) following the TULIP theorem. Simulations of Z-value distribution is known to fit with a Gumbel law. This remarkable property was not demonstrated and had no obvious biological support. Results: We built a model of evolution of sequences based on aging, as meant in Reliability Theory, using the fact that the amount of information sha...

• Type: Journal
• Year: 2008
• Where: BMCBI
• Authors: Olivier Bastien, Eric Maréchal
• Keywords: Alignment Scores, Biological Sequences, BMCBI 2008, Sequences