Biotechnology and Bioinformatics (1+1)

1.2.4. Classification of genes

Genes are the parts of the DNA which contains functional code, the templates of all the bits that make a living organism.

Functional sequence s only represents a small fraction of the total genome , for example around 3% in humans.

The rest is made up of what has been called ‘ junk DNA ’ whether all of it is really ‘junk’ is not known, but it is possible that much of it will have some function in the organism.

Some of this junk DNA consists of Psudogenes, genes that for some reason or another have become non-functional.

Much of the junk DNA is probably the relics of genes which have become non-functional during evolution or bits of DNA inserted into the genome by viruses .

Providing the junk DNA has no detrimental effect on the organism, it can mutate, move, or make copies of itself.

Other non-coding DNA consist of dispersed or clustered repeated sequences of varying length, from one base pair (bp) to thousands of bases (kilobases, kb) in length.

The dispersed repeated sequences occur as copies spread across the genome and can be categorized as long or short interspersed nuclear elements (LINE or SINE), long terminal repeats (LTR) and DNA transposons .

The clustered repeated sequences, where the repeated sequences occurs in tandem copies, are called as satellites, minisatellites or microsatellites depending on the length of the repeat unit, and these turned out to be useful genetic marker s.

These repeated elements can constitute up to 40% of the genome.