Genome organization

Human genome includes genetic material DNA in its cells. Human genomes are broadly classified in to two types, namely, nuclear genome and mitochondrial genome. The nuclear genome and mitochondrial genome are about 3200 Mbp and 16.6 kb in their lengths. Based on the cot curve analysis by shearing DNA, it is interpreted that nuclear genome are divided into repeated sequential DNA.

Repeated class of nuclear DNA

Nuclear DNA is broadly classified in to three major types.

• Unique DNA
  • Conserved coding regions
  • Non conserved coding regions
• Moderately repeated DNA
  • Transposon
• Highly repeated DNA
  • Heterochromatin
  • Micro satellites
  • Transposon families

Highly repeated sequence

DNA sequences which are very short and tandemly repeated are highly conserved. It is present near centromere or chromosomes short arms. For instance, heterochromatin consists of highly repeated sequence of DNA. Shorter DNA is no longer involved in transcribing process.

Types of highly repeated sequence

• Satellite DNA
• Mini satellites
• Micro satellites

Satellite DNA: DNA that is repeated tandemly with varying densities is referred as Satellite DNA. They do not have unique base composition unlike the wild DNA has. It is located in centromere section of chromosomes. Three major types of satellite DNA found in human are I, II and III.

Mini satellites: Short base pair DNA of 10-30 bp in length which is tandemly repeated is referred as mini satellites. It is located in telomere region of chromosomes. When mini satellites are found in more number of people, it is referred as hypervariable. Hypervariable mini satellites are also referred as variable number tandem repeats (VNTRs). They are used in DNA fingerprinting applications.

Micro satellites: DNA base pair of 2-5 bp is referred as micro satellites or SSRs. It is found located throughout the genome. It is used as a source for genome map development.

Moderately repeated DNA sequence

Transposons are moderately repeated DNA sequence. They are of two types, namely, retrotransposons which replicate through RNA and DNA transposons which move to new locations by piercing DNA fragment from one location and are inserted into new location.