Junk DNA
BMJ 2005; 330 doi: https://doi.org/10.1136/sbmj.0505192 (Published 01 May 2005) Cite this as: BMJ 2005;330:0505192
- Raghav chawla, fifth year medical student1
- 1University of Lausanne, Switzerland
Pub Medic:Impress your mates at the pub with your startling repertoire of esoteric medical knowledge.
“Today, we are learning the language in which God created life,” US President Bill Clinton said on 26 June 2000. The initial sequencing of the human genome had historically been completed.1
Eight months on, two research teams published their draft versions of the sequence.23 In an article accompanying the publication in Nature, David Baltimore, remarked, “For conceptual impact, it does not hold a candle to Watson and Crick's 1953 paper describing the structure of DNA. Nonetheless, it is a seminal paper, launching the era of post-genomic science.” 45
Our genome
The human genome consists of about three billion base pairs, packaged into 23 pairs of chromosomes. Only 1% codes for protein - “coding DNA.”6 The remaining 99% is non-coding DNA; it is half repetitive and half non-repetitive sequences.7
Most repetitive sequences are scattered randomly throughout the genome. They arise through segmental duplication or, more commonly, through transposition (box 1).8 Some may carry pseudogenes, degenerated non-functional genes. Conversely, a limited number of repeats appear to be clustered in tandem. Many of these “DNA satellites” are in centromeric and telomeric chromosomal regions.6
Box 1: Transposition6
Transposition, in which DNA sequences, referred to as transposons or “jumping” DNA, are excised or copied from one location of a chromosome and reinserted into another location …
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