Before revision:  This chapter introduces methods developed by the Rfam database for identifying "families" of homologous ncRNAs  from single "seed" sequences using manually curated  alignments to build powerful statistical models  known as covariance models (CMs)  .
After revision:  This chapter introduces methods developed by the Rfam database for identifying "families" of homologous ncRNAs from single "seed" sequences using manually curated alignments to build powerful statistical models of sequence and structure conservation known as covariance models (CMs) .