(b) : In certain development stages the polytene chromosomes bear conspicuous swellings called chromosome puffs. The larger swellings are called Balbiani rings. In the region of a puff or Balbiani ring, the $DNA$ strands uncoil, become active and produce number of copies of $mRNA$. The $mRNAs$ may remain temporarily stored in the puff and they may undergo transcription to form proteins. Thus, Balbiani rings are the sites of $RNA$ and protein synthesis.