COS 126

Theory of Computation Exercises
Assignment


  1. Huntington's disease diagnostic. Huntington's disease (HD) is an inherited and fatal neurological disorder. Although there is currently no cure, in 1993 scientists discovered a very accurate genetic test. The gene that causes Huntington's disease is located on the short arm of chromosome 4, and it has a variable number of (consecutive) repeats of the CAG trinucleotide. These stuttering repeats lead to an excess in the amount of the amino acid glutamine in the protein huntingtin. The normal range of CAG repeats is between 10 and 35. Individuals with HD may have between 36 and 180 repeats. Doctors can use a simple PCR-based DNA test, count the number of repeats, and inform patients whether they are at risk.

     repeats   diagnosis 
    0–9  not human
    10–35  normal
    36–39  high risk
      40–180     Huntington's disease  
    181–∞ not human

    Write a data type Huntingtons that takes a human DNA sequence and determines whether the patient is at risk for HD by determining the maximum number of CAG repeats. Implement the following API:

    public class Huntingtons
    ---------------------------------------------------------------------------
           Huntingtons(String dna)  // construct a new object using given DNA
       int maxRepeats()             // return the maximum number of CAG repeats
    String diagnosis()              // return the diagnosis as a String
    

    For full credit, your program must use regular expressions to find the CAG repeats. Also, include a test client main() that takes a sequence of filenames as command-line arguments, and outputs the maximum number of CAG repeats and the corresponding medical diagnosis for each.

    The data file format will consist of a sequence of the characters 'A', 'C', 'T', 'G', or 'N', along with arbitrary amounts of intervening whitespace (which you will need to strip out before invoking the constructor). For example, the DNA sequences in test4.txt, test5.txt, test64.txt, chromosome4-hd.txt, and chromosome4-healthy.txt have CAG repeats of sizes 4, 5, 64, 79, and 19, respectively.

    % more test4.txt                         % more test64.txt
    TTTTTTTTTT TTTTTTTTTT TTTTTTTTCA         TTTTTTTTTT TTTTTTTTTT TTTTTTTTTT
    GCAGCAGCAG TTTCAGCAGT TTTTTTTTTT         TTTTTTTTTT TTTTTTTTTT TTCAGCAGCA
    TTTTTTTTTT TTTTTTTTTT TTTTTTTTTT         GCAGCAGCAG CAGCAGCAGC AGCAGCAGCA
    TTTCAGTTTT TTTTTTTTTT T                  GCAGCAGCAG CAGCAGCAGC AGCAGCAGCA
                                             GCAGCAGCAG CAGCAGCAGC AGCAGCAGCA
    % more test5.txt                         GCAGCAGCAG CAGCAGCAGC AGCAGCAGCA
    TTTTTTTTTT TTTTTTTTTT TTTTTTTTNA         GCAGCAGCAG CAGCAGCAGC AGCAGCAGCA
    GCNGNAGCAN CAGTTTCAGC AGCAGTTTTT         GCAGCAGCAG CAGCAGCAGC AGCAGCAGCA
    TTTTTTTTTT TTTTTTTTTT TTTTTTTTTT         GCAGTTTTTT TTTTTTTTTT TTTTTTTTTT
    TTTCAGTTTT TTTTTTTTTT T                  TTTTTTTTTT TTTTTTTTTT TTTTTTTTTT
    
    % java Huntingtons test4.txt test5.txt test64.txt chromosome4-hd.txt chromosome4-healthy.txt
    test4.txt
    max number of CAG repeats = 4
    not human
    
    test5.txt
    max number of CAG repeats = 5
    not human
    
    test64.txt
    max number of CAG repeats = 64
    Huntington's disease
    
    chromosome4-hd.txt
    max number of CAG repeats = 79
    Huntington's disease
    
    chromosome4-healthy.txt
    max number of CAG repeats = 19
    normal
    


  2. Turing machine. Design a Turing machine comparator.tur (in the file format specified below) that takes as input two binary integers (separated by the > symbol) and terminates in a yes state if the first integer is strictly greater than the second one, and a no state otherwise. Use only the following four symbols: 0 1 > #. Use this Turing machine simulator to develop your machine.

    As an example, The Turing machine binaryadder.tur takes as input two binary integers (separated by the + symbol) and terminates with the sum written in the tape.

    % more binaryadder.tur
    title
    Binary Adder
    
    description
    Kevin Wayne, wayne, P01
    Add two binary numbers, and
    leave the result on the tape.
    
    vertices
    2 R 0.25 0.75
    0 L 0.25 0.25
    1 L 0.75 0.25
    3 L 0.75 0.75
    4 R 0.40 0.50
    5 H 0.60 0.50
    
    edges
    0 0 0 1  135
    0 1 1 0
    0 4 + #
    1 3 + +
    2 0 # #
    3 2 # 1  0.2
    3 2 0 1 -0.2
    3 3 1 0 -30
    4 4 1 # -135
    4 5 # #
    
    tapes
    [1] 0 1 0 + 1 1 1 1
    [1] 0 0 + 1 1 1
    [1] 1 0 0 + 1 1
    [1] 0 1 0 + 1 0 0 1 0 1 
    

    The data file is divided into 5 sections (title, description, vertices, edges, tapes), and each section begins with the corresponding name. Each vertex (state) is specified with 4 required values: its name (a string), its type (L, R, Y, N, H), and its x- and y-coordinates (between 0 and 1). The first state listed is the start state. Each edge (transition) is specified with 4 required values: the starting state, the ending state, the symbol to read, and the symbol to write. An optional 5th parameter specifies the curvature with which to draw the edge (straight line by default). Each sample input tape is specified by listing its symbols, separated by spaces. The tape head starts at the symbol delimited by square braces - for this assignment, it should always be the leftmost non-blank character.

    Submission. Submit Huntingtons.java and comparator.tur. Also, submit a readme.txt and answer any questions.

    Extra credit. If you based your comparator on binaryadder.tur, then it is very similar to a subtractor. Unfortunately, it would take more than 2n steps to subtract two n-bit numbers. Your challenge is to design a Turing machine that subtracts two positive n-bit numbers in time proportional to n2. Assume the left number on the tape is always larger than or equal to the right number, so the difference will always be greater than or equal to zero. However, do not assume that the two numbers always have the same number of bits. Name your file efficientSubtractor.tur and submit it as an Additional File.


    This assignment was created by Kevin Wayne.
    Copyright © 2004.