Oh, I see. Then maybe this can help you: 
#!/usr/bin/perl
use warnings;
use strict;

my %matrix;
my @symbols = qw/A     R      N      D      C      Q      E      G    
+  H      I      L      K      M      F      P      S      T      W   
+   Y      V/;
my @table = (.9799, .0002, .0009, .0010, .0003, .0008, .0017, .0021, .
+0002, .0006, .0004, .0002, .0006, .0002, .0022, .0035, .0032, .0000, 
+.0002, .0018,
             .0001, .9929, .0001, .0000, .0001, .0010, .0000, .0000, .
+0010, .0003, .0001, .0019, .0004, .0001, .0004, .0006, .0001, .0008, 
+.0000, .0001,
             .0004, .0001, .9867, .0036, .0000, .0004, .0006, .0006, .
+0021, .0003, .0001, .0013, .0000, .0001, .0002, .0020, .0009, .0001, 
+.0004, .0001,
             .0006, .0000, .0042, .9869, .0000, .0006, .0053, .0006, .
+0004, .0001, .0000, .0003, .0000, .0000, .0001, .0005, .0003, .0000, 
+.0000, .0001,
             .0001, .0001, .0000, .0000, .9987, .0000, .0000, .0000, .
+0001, .0001, .0000, .0000, .0000, .0000, .0001, .0005, .0001, .0000, 
+.0000, .0002,
             .0003, .0010, .0004, .0005, .0000, .9901, .0027, .0001, .
+0024, .0001, .0003, .0006, .0004, .0000, .0006, .0002, .0002, .0000, 
+.0000, .0001,
             .0010, .0000, .0007, .0056, .0000, .0035, .9865, .0004, .
+0002, .0003, .0001, .0004, .0001, .0000, .0003, .0004, .0002, .0000, 
+.0001, .0002,
             .0021, .0001, .0012, .0011, .0001, .0003, .0007, .9906, .
+0001, .0000, .0001, .0002, .0001, .0001, .0003, .0021, .0003, .0000, 
+.0000, .0005,
             .0001, .0008, .0018, .0003, .0001, .0020, .0001, .0000, .
+9933, .0000, .0001, .0001, .0000, .0002, .0003, .0001, .0001, .0001, 
+.0004, .0001,
             .0002, .0002, .0003, .0001, .0002, .0001, .0002, .0000, .
+0000, .9915, .0009, .0002, .0012, .0007, .0000, .0001, .0007, .0000, 
+.0001, .0033,
             .0003, .0001, .0003, .0000, .0000, .0006, .0001, .0001, .
+0004, .0022, .9871, .0002, .0045, .0013, .0003, .0001, .0003, .0004, 
+.0002, .0015,
             .0002, .0037, .0025, .0006, .0000, .0012, .0007, .0002, .
+0002, .0004, .0001, .9858, .0020, .0000, .0003, .0008, .0011, .0000, 
+.0001, .0001,
             .0001, .0001, .0000, .0000, .0000, .0002, .0000, .0000, .
+0000, .0005, .0009, .0005, .9968, .0001, .0000, .0001, .0002, .0000, 
+.0000, .0005,
             .0001, .0001, .0001, .0000, .0000, .0000, .0000, .0001, .
+0002, .0008, .0006, .0000, .0004, .9944, .0000, .0000, .0001, .0003, 
+.0028, .0000,
             .0013, .0005, .0002, .0001, .0001, .0008, .0003, .0002, .
+0005, .0001, .0002, .0002, .0001, .0001, .9935, .0012, .0004, .0000, 
+.0000, .0002,
             .0028, .0011, .0034, .0007, .0011, .0004, .0006, .0016, .
+0002, .0002, .0001, .0007, .0004, .0003, .0017, .9800, .0038, .0005, 
+.0002, .0002,
             .0022, .0002, .0013, .0004, .0001, .0003, .0002, .0002, .
+0001, .0011, .0002, .0008, .0006, .0001, .0005, .0032, .9874, .0000, 
+.0002, .0009,
             .0000, .0002, .0000, .0000, .0000, .0000, .0000, .0000, .
+0000, .0000, .0000, .0000, .0000, .0001, .0000, .0001, .0000, .9995, 
+.0001, .0000,
             .0001, .0000, .0003, .0000, .0003, .0000, .0001, .0000, .
+0004, .0001, .0001, .0000, .0000, .0021, .0000, .0001, .0001, .0002, 
+.9960, .0001,
             .0013, .0002, .0001, .0001, .0003, .0002, .0002, .0003, .
+0003, .0057, .0011, .0001, .0017, .0001, .0003, .0002, .0010, .0000, 
+.0002, .9866);

for my $column (@symbols) {
    for my $row (@symbols) {
        $matrix{$column}{$row} = shift @table;
    }
}

my $string;
$string = 'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA'
+;
#$string = 'SVEQRISTDIGQAYQLQGLGSNLRSIRSKTGAGEVNYIDAAKSVNDNQLLAEIG';

print "$string\n";
print map mutate($_), split //, $string;
print "\n";

sub mutate {
    my $char = shift;
    my $rand = rand;
    my $result = 0;
    while ($rand > 0 and $result <= @symbols) {
        $rand -= $matrix{$char}{$symbols[$result++]};
    }
    return $symbols[$result - 1];
}

[download]
Update: bugfix.

In reply to Re^3: string mutation script behaving erraticaly by choroba
in thread string mutation script behaving erraticaly by zing

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.