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Local sequence alignment. Often two DNA sequences are significantly different, but contain regions that are very similar and are highly conserved. Design an algorithm that takes an input two strings x[1Kn]and y[1Km]and a scoring matrix (as defined in Exercise 6.26), and outputs substrings x'andy'of x and y respectively, that have the highest-scoring alignment over all pairs of such substrings. Your algorithm should take time O(mn).

Short Answer

Expert verified

The complexity of the program is Omn

Step by step solution

01

Local Sequence Alignment

The total scoring alignment is the cost of editing the strings using insertion, deletion, or gap penalties.

Suppose the given strings are x=x1,x2,Kxnandy=y1,y2,Kym.

The first step is to determine the similarity score of the elementsa,b and the gap penalty of length k.

In the next step the first row and column of the scoring matrix M of size role="math" localid="1658918665081" n+1times m+1to zero Then in the next step, the scoring matrix is filled.

Then tracing back from the highest score to zero in the scoring matrix gives the best alignment.

02

Step 2:Give Algorithm

Algorithm:

The algorithm can be written as given below:

a,b- score

Gk- gap penalty of length k

Mn+1m+1- scoring matrix

for o=0ton

M01=0

for o=0 to m

M10=0

for o=1 to n

for p=1 to n

Mop=max1Mo-1p-1+ao,bpmaxk1,Mo-kp-Gkmaxl1,Mop-1-Gk

Traceback from highest alignment score to 0.

03

Step 3:Explain Algorithm

Explanation:

Mopis a optimal score of aligning.

There are only a polynomial number of subproblems.

Every subproblems can be solved easily by solving smaller subproblems.

See, in step-7 we have three cases. first case is xo=ypsecond case is, xo aligns to a gap and, third case is ypaligns to a gap.

The calculated scoring matrix is of size

So, the complexity of the program is Onmo=

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Most popular questions from this chapter

The garage sale problem (courtesy of Professor Lofti Zadeh). On a given Sunday morning, there are n garage sales going on, g1,g2,g3............gn. For each garage sale gj, you have an estimate of its value to you, vj. For any two garage sales you have an estimate of the transportation cost dijof getting from gito gj. You are also given the costs d0jand dj0of going between your home and each garage sale. You want to find a tour of a subset of the given garage sales, starting and ending at home, that maximizes your total benefit minus your total transportation costs. Give an algorithm that solves this problem in time O(n22n).

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Evolutionary history is commonly represented by a tree whose leaves are the different species, whose root is their common ancestor, and whose internal branches represent speciation events (that is, moments when a new species broke off from an existing one). Thus we need to find the following:

鈥 An evolutionary tree with the given species at the leaves.

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localid="1659249441524" score(T)=(u.v)E(T)(numberofpositionsonwhichs(u)ands(v)disagree)

Finding the highest-score tree is a difficult problem. Here we will consider just a small part of it: suppose we know the structure of the tree, and we want to fill in the sequences s(u) of the internal nodes u. Here鈥檚 an example with k=4 and n=5:


(a) In this particular example, there are several maximum parsimony reconstructions of the internal node sequences. Find one of them.

(b) Give an efficient (in terms of n and k ) algorithm for this task. (Hint: Even though the sequences might be long, you can do just one position at a time.)

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Give a dynamic programming algorithm that, given the locations of m cuts in a string of length , finds the minimum cost of breaking the string into m +1 pieces.

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then15,30,10 is a contiguous subsequence but5,15,40 is not. Give a linear-time algorithm for the following task:Input: A list of numbers a1,a2,...,an.

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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.

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Show how to do this efficiently.

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