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Exon chaining.Each gene corresponds to a subregion of the overall genome (the DNA sequence); however, part of this region might be 鈥渏unk DNA.鈥 Frequently, a gene consists of several pieces called exons, which are separated by junk fragments called introns. This complicates the process of identifying genes in a newly sequenced genome.

Suppose we have a new DNA sequence and we want to check whether a certain gene (a string) is present in it. Because we cannot hope that the gene will be a contiguous subsequence, we look for partial matches鈥攆ragments of the DNA that are also present in the gene (actually, even these partial matches will be approximate, not perfect). We then attempt to assemble these fragments.

Let x 1Kndenote the DNA sequence. Each partial match can be represented by a triple li,ri,wi, where xliKriis the fragment and is a weight

representing the strength of the match (it might be a local alignment score or some other statistical quantity). Many of these potential matches could be false, so the goal is to find a subset of the triples that are consistent (nonoverlapping) and have a maximum total weight.

Show how to do this efficiently.

Short Answer

Expert verified

Dynamic programming solves the problem in On

Step by step solution

01

Step 1:Explain Exon Chaining

The DNA sequence or genome is written asx1Kn

Each partial matching given represents the starting and the weight of the match.

From these given sets of intervals, the maximum chain of intervals in required.

The greedy solution to this problem repeats the process of taking the chain with the highest scores first and then the largest left in the range until no more chains can be taken. Then sum the taken chains to get the maximum score.

But by constructing a graph, this problem can be solved in Ontime complexity.

02

Step 2:Give Algorithm

Algorithm is as follows,

With a graph GV,E, the algorithm is given as follows:

(G, n)

for i= 1 to 2n

resi=0

for i = 1 to 2n

if viin G corresponds to right end l

jileft end index of vertex for l

wi-weight

resj=maxresj+wi,resj-1

else

resi=resi-1

return res2n

03

Explain the algorithm

Explanation:

The Exon chaining problem can be solved using dynamic programming in a graph.

And that same approach is provided above.

The problem for n interval can be solved using 2nvertices in graph.

Assume that the set of left and right interval ends is sorted into ascending order.

And all positions are definite. This forms an ordered array of vertices.

There are 3n-1edges in the graph. In the algorithm, residenotes the length of the longest path ending at vertex vi in the graph.

Therefore the final solution is res2n

Thus, dynamic programming solves the problem in O (n)

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