The sequence of vertebrate genome is expressed by RNA splicing producing mRNA. Interpreting the genome requires understanding the sequences recognized by the nuclear factors and spliceosomia executing removal of introns. The status of this area of science will be reviewed. Conversely, genome sequences can be searched for sequences which specify RNA splicing and are common of many genes. The availability of genome sequences from a variety of species will make the latter approach much more powerful. The recently discovered RNA interference (RNAi) process is evolutionarily old and related processes are important for control of expression of repetitive genes in some organisms. RNAi can be initiated by conversion of double strand RNA into 21-23 nucleotide RNAs which can base pair with mRNAs and direct their cleavage. These short RNAs may also direct silencing of genes by other mechanisms. Over half of the genome of many organisms is composed of repetitive sequences and it is possible that RNAi may silence these sequences.