@dna = 'accatgagctgtacgtagcatctgagcgcgcatgactgtgactgacgtaggcagca';
my $dna = join ('', @dna);
my $movement = 3;

for (my $pos = 10; $pos <= @dna; $pos +=$movement+1)  {
     substr ($dna, $pos,0, "\n");
}
                                                                                                     
my @windows;
push @windows, $dna;
                                                                                                     
print "@windows\n";