The vast majority of the human genome is comprised of non-coding DNA sequences

• Protein-encoding genes only account for approximately 1.5% of the total DNA sequence
  

Historically referred to as ‘junk DNA’, these non-coding regions are now recognised to serve other important functions, including:

• Satellite DNA sequences (such as short tandem repeats) are commonly used in DNA profiling to differentiate between individuals

• Telomeres (the ends of chromosomes) have repetitive sequences that prevent chromosomal deterioration during replication

• Introns are non-coding sequences within eukaryotic protein-encoding genes (removed during RNA processing)

• Non-coding genes produce RNA sequences that do not directly code for proteins (such as tRNA and rRNA genes)

• Gene regulatory sequences function to moderate transcriptional activity (e.g. enhancer and silencer sequences)