The genome of an organism is its hereditary information encoded in DNA.
The genome is made up of genes that code for proteins and other DNA sequences that do not code for proteins.
Most of the eukaryotic genome consists of non-coding sequences. For example, the human genome consists of around three billion nucleotides but only a small component of this actually codes for proteins.
These coding sequences make up less than two per cent of the genome.
The rest of the genome is made up of non-coding sequences.
Some of these non-coding sequences are involved in regulating the transcription of proteins, some are transcribed to RNA but are never translated into protein, for example tRNA, rRNA and other RNA fragments.
Many non-coding sequences have no known function.