docs: def get_max_position(self, chrom):
          """Get the last position observed on a chromosome in the database
          
          Args:
              chrom(str)
          
          Returns:
              end(int): The largest end position found
              
          """
          res = self.db.variant.find({'chrom':chrom}, {'_id':0, 'end':1}).sort([('end', DESCENDING)]).limit(1)
          end = 0
          for variant in res:
              end = variant['end']
          return end