my @dna = split("","ATCTGCG"); 
my @comp = split("","TCTGCAA"); 
my %pairs = qw(A T T A G C C G); 
foreach (0..$#dna) {
	my $d = $dna[$_];
	my $c = $comp[$_];
	print "$_: $d - $c is a mispair\n" unless ($pairs{$d}  eq $c);
}