Types of DNA

• Single copy DNA forms 75% of the genome. This includes the DNA that codes for proteins in the exons. Most of the DNA is in introns. Thus, only about 10% of the genome is contained in exons that actually encode the proteins, and only about 10% of this is functioning at any one time in the cell.

• Dispersed repetitive DNA forms 15% of the genome. This includes DNA sequences that are repeated many times.

• Satellite DNA comprises 10% of the genome. This includes tandem repeats of DNA sequences and includes three forms:

  • Alpha satellite DNA - these tandem repeats occur near centromeres

  • Minisatellite DNA - small blocks of tandem repeats

  • Microsatellite DNA - tiny blocks of tandem repeats