code: def add_qtl_to_marker(marker, qtls):
      
      cnt = 0
      for qtl in qtls:
          if qtl[-1] == marker[0]:
              cnt = cnt + 1
  
      marker.append(str(cnt))
      return marker
docs: Add the number of QTLs found for a given marker.
  
      :arg marker, the marker we are looking for the QTL's.
      :arg qtls, the list of all QTLs found.