code: def alleles_to_retrieve(df):
      
      contig_blastn_records = defaultdict(list)
      markers = df.marker.unique()
      for m in markers:
          dfsub = df[df.marker == m]
          for i, r in dfsub.iterrows():
              if r.coverage < 1.0:
                  contig_blastn_records[r.stitle].append(r)
              break
      return contig_blastn_records
docs: Alleles to retrieve from genome fasta
  
      Get a dict of the genome fasta contig title to a list of blastn results of the allele sequences that must be
      retrieved from the genome contig.
  
      Args:
          df (pandas.DataFrame): blastn results dataframe
  
      Returns:
          {str:[pandas.Series]}: dict of contig title (header name) to list of top blastn result records for each marker
              for which the allele sequence must be retrieved from the original sequence.