On the number of alignments ofk sequences
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Numerous studies by molecular biologists concern the relationships between several long DNA sequences, which are listed in rows with some gaps inserted and with similar positions aligned vertically. This motivates our interest in estimating the number of possible arrangements of such sequences. We say that ak sequence alignment of sizen is obtained by inserting some (or no) 0's intok sequences ofn 1's so that every sequence has the same length and so that there is no position which is 0 in allk sequences. We show by a combinatorial argument that for any fixedk≥1, the numberf(k, n) ofk alignments of lengthn grows like (c k ) n as n → ∞, wherec k = (21/k − 1) -k . A multi-dimensional saddle-point method is used to give a more precise estimate forf(k, n).
KeywordsSequence Alignment Precise Estimate Similar Position Molecular Biologist Combinatorial Argument
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