Fact Box: Junk DNA

May 17, 2013

Scientists from the Centre for Cellular and Molecular Biology (CCMB) have found in a study that all the non-coding part of human DNA is not junk. While more than 50% of the non-coding DNA was repetitive, Simple Sequence Repeats (SSRs) account for about 3% of the human genome.
What is Junk DNA?
Human has 100 billion km of total DNA, enough to reach sun and come back 300 times. But of the 3.3 billion nucleotides of human genome, less than 2% code for proteins while the remaining 98% is non-coding in nature and generally described as “junk DNA”.
What is the importance of Junk DNA according to scientists?
Scientists have found that one of the SSRs, the GATA repeat had significant regulatory role in gene expression by functioning as a boundary, separating functional domains of genome. The accumulation of non-coding part of the genome (whose function is still unknown) appears to be the driving force behind the evolution of complexity in living organisms. This indicates that the biological complexity had not evolved by the addition of more genes to the genome but by more sophisticated regulation of the pre-existing genes.
SSRs, including GATA repeats were known to show polymorphisms-small size variations in size of the repeat at different loci in the genome within a population. Such variations were the basis of DNA finger printing that could establish the genetic identity of a person.