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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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Most popular questions from this chapter

You are given a convex polygon P on n vertices in the plane (specified by their x and y coordinates). A triangulation of P is a collection of n-3diagonals of such that no two diagonals intersect (except possibly at their endpoints). Notice that a triangulation splits the polygon鈥檚 interior into n-2 disjoint triangles. The cost of a triangulation is the sum of the lengths of the diagonals in it. Give an efficient algorithm for finding a triangulation of minimum cost. (Hint: Label the vertices of P by 1,....,n, starting from an arbitrary vertex and walking clockwise. For 1i<jn, let the subproblem A(i,j)denote the minimum cost triangulation of the polygon spanned by vertices i,i+1,...,j.).

Cutting cloth. You are given a rectangular piece of cloth with dimensions XY, whereX and Yare positive integers, and a list of products that can be made using the cloth. For each producti[1,n] you know that a rectangle of cloth of dimensionsaibi is needed and that the final selling price of the product is ci. Assume the,ai biandci are all positive integers. You have a machine that can cut any rectangular piece of cloth into two pieces either horizontally or vertically. Design an algorithm that determines the best return on theXY piece of cloth, that is, a strategy for cutting the cloth so that the products made from the resulting pieces give the maximum sum of selling prices. You are free to make as many copies of a given product as you wish, or none if desired.

Consider the following variation on the change-making problem (Exercise 6.17): you are given denominations x1,x2,...,xn, and you want to make change for a value v, but you are allowed to use each denomination at most once. For instance, if the denominations are 1,5,10,20,then you can make change for 16=1+15and for 31=1+10+20but not for 40(because you can鈥檛 use 20 twice).

Input: Positive integers; x1,x2,...,xnanother integer v.

Output: Can you make change for v, using each denominationxi at most once?Show how to solve this problem in time O(nV).

Alignment with gap penalties. The alignment algorithm of Exercise 6.26 helps to identify DNA sequences that are close to one another. The discrepancies between these closely matched sequences are often caused by errors in DNA replication. However, a closer look at the biological replication process reveals that the scoring function we considered earlier has a qualitative problem: nature often inserts or removes entire substrings of nucleotides (creating long gaps), rather than editing just one position at a time. Therefore, the penalty for a gap of length 10 should not be 10 times the penalty for a gap of length 1, but something significantly smaller.

Repeat Exercise 6.26, but this time use a modified scoring function in which the penalty for a gap of length k is c0 + c1k, where c0 and c1 are given constants (and c0 is larger than c1).

Given an unlimited supply of coins of denominations, we wish to make change for a value ; that is, we wish to find a set of coins whose total value is . This might not be possible: for instance, if the denominations are and 10 then we can make change for 15 but not for 12. Give an dynamic-programming algorithm for the following problem.Input:,; .Question: Is it possible to make change for using coins of denominations ?

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