Definition: “Junk DNA” refers to regions of DNA that do not code for proteins and were once believed to have no biological function.
Key Facts
Percentage in Humans: About 98–99% of the human genome is non-coding DNA.
The term “junk DNA” is misleading — many of these regions have regulatory or structural roles.
Types of Non-coding DNA
Introns: Non-coding sequences within genes removed during mRNA processing.
Regulatory Sequences: Control gene activity – promoters, enhancers, silencers.
Repetitive DNA: Satellite DNA, minisatellites, microsatellites.
Transposons (Jumping Genes): Mobile DNA elements – LINEs, SINEs.
Pseudogenes: Defunct or inactive copies of functional genes.
Evolving Understanding
Earlier thought to be useless; now known to play roles in:
oGene regulation,
oChromatin structure,
oGenome stability.
The ENCODE Project (2012) found that a significant portion of “junk DNA” is biochemically active.
Functions Identified
Regulating gene expression (turning genes on/off).
Maintaining chromosomal structure.
Producing non-coding RNAs (microRNAs, lncRNAs) that control other genes.
Providing evolutionary raw material for genetic variation and innovation.\
IAS-2026 - OPTIONAL / GEOGRAPHY / PUBLIC ADMINISTRATION / SOCIOLOGY / ANTHROPOLOGY / ORIENTATION ON 03 & 04-10-2025 
