A DNA sequence that codes for ribosomal RNA (rRNA) is called ribosomal DNA. There is from 50 to 5,000 sets of rRNA genes in eukaryotic genome, since the rRNA is critical for making ribosome to carry out protein synthesis. rRNA has an active role in recognizing conserved portions of mRNAs and tRNAs, so it must be made in sufficient quantities to keep up with a cell's demands for proteins.
