sub reverse_complement {
my $dna = shift;
# reverse the DNA sequence
my $revcomp = reverse($dna);
# complement the reversed DNA sequence
$revcomp =~ tr/ACGTacgtRYKMSWrykmswBDHVbdhv/TGCAtgcaYRMKSWyrmkswVHDBvhdb/;
return $revcomp;
}