diff --git a/utils/check_tandem_stop_codon_usage.py b/utils/check_tandem_stop_codon_usage.py
new file mode 100755
index 0000000..b8798d4
--- /dev/null
+++ b/utils/check_tandem_stop_codon_usage.py
@@ -0,0 +1,107 @@
+#!/usr/bin/env python
+import pandas as pd
+from Bio import SeqIO
+import sys
+import argparse
+
+
+def read_gff(filepath):
+    """
+    Reads gene annotations in GFF format, only keep those that were annotated as isoforms, i.e., dual-coding
+    :param filepath: str, path to file
+    :return: pd.DataFrame, gene annotations
+    """
+    df = pd.read_csv(filepath, sep='\t',
+                     header=None, comment='#',
+                     names=['sequence', 'source', 'feature', 'start',
+                            'end', 'logodd', 'strand', 'phase', 'attributes'])
+    df['gene_id'] = [attr.split(';')[0] for attr in df.attributes.values]
+    df['isoform'] = [True if '.' in gid else False for gid in df.gene_id.values]
+    df = df[df.isoform] 
+    df.reset_index(drop=True, inplace=True)
+    return df
+
+
+def read_sequence(filepath):
+    """
+    Parse genomic sequence stored in Fasta format
+    :param filepath: str, path to fasta file
+    :return: dict, genomic sequences
+    """
+    records = SeqIO.to_dict(SeqIO.parse(filepath, 'fasta'))
+    return records
+
+
+def extract_sequences_following_stop(df, sequence):
+    """
+    Extract 30 bp following a stop codon
+    :param df: pd.DataFrame, gene annotations
+    :param sequence: dict, corresponding genomic sequences
+    :return: list, list, list, sequences following stop codon predicted by both code models, code model 11,
+                               alternative code model with stop codon reassignment
+    """
+    sequences_11 = []
+    sequences_alt = []
+    sequences_all = []
+    for i in range(df.shape[0]):
+        start = df.loc[i, 'start']
+        end = df.loc[i, 'end']
+        strand = df.loc[i, 'strand']
+        contig = sequence[df.loc[i, 'sequence']]
+        source = df.loc[i, 'source']
+        if strand == '+':
+            seq = contig[end -3: end+30]
+        elif strand == '-':
+            seq = contig[start -31: start +2].reverse_complement()
+        if len(seq) < 33:
+           continue
+        sequences_all.append(seq)
+        if source.endswith('11'):
+            sequences_11.append(seq)
+        else:
+            sequences_alt.append(seq)
+    return sequences_all, sequences_11, sequences_alt
+
+
+def write_sequences_to_file(sequences, output_file):
+    """
+    Writes genomic sequences to a txt file
+    :param sequences: list, DNA sequences
+    :param output_file: str, path to output file
+    """
+    with open(output_file, 'w') as out:
+        for seq in sequences:
+            out.write(str(seq.seq) + '\n')
+    out.close()    
+
+
+def main(argv):
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--genomes', help='File specifying one genome per line that should be included in analysis')
+    parser.add_argument('--mgcod_results', help='Path to directory containing MgCod annotations')
+    args = parser.parse_args()
+    genomes  = []
+    gffs = []
+    with open(args.genomes, 'r') as fp:
+        for line in fp:
+            genomes.append(line.strip())
+            gffs.append(args.mgcod_results + line.strip().split('/')[-1].replace('.fna', '.gff')) 
+    fp.close()
+    sequences_11 = []
+    sequences_alt = []
+    sequences_all = []
+
+    for gff, genome in zip(gffs, genomes):
+        df = read_gff(gff)
+        records = read_sequence(genome)
+        seq_all, seq_11, seq_alt = extract_sequences_following_stop(df, records)
+        sequences_all.extend(seq_all)
+        sequences_11.extend(seq_11)
+        sequences_alt.extend(seq_alt)
+    write_sequences_to_file(sequences_all, 'sequences_following_stop_all.fasta')
+    write_sequences_to_file(sequences_11, 'sequences_following_stop_11.fasta')
+    write_sequences_to_file(sequences_alt, 'sequences_following_stop_alt.fasta')
+
+
+if __name__ == '__main__':
+    main(sys.argv[1:])