Question

How has DNA accumulated a lot of non-coding DNA?

Answer 1

DNA may comprise of coding sequences which can code for proteins, like the exons.

Many eukaryotic gene contain, regions of “expressed sequence” or exons, which code for proteins.

Non-coding DNA include positions of DNA which does not code for protein. These are more in eukaryotic genome.

• Non-coding regions include intervening sequences or introns, regulatory sequences as operator, promoter, enhancer sequences and repetitive DNA sequences or repeats (tandem repeats, interspersed sequences).
• The non-coding portions are generally removed during splicing.
• But by variation in the splicing process, may retain some of the non-coding potions.
• The process of alternative splicing, the gene products may be modified. In alternate splicing alternative introns may be removed to get a different sequence producing an alternative protein.
• Thus, the sequences that are spliced, or the retained sequences after the splicing, will express differently specifying different cell types.
• This differential splicing (alternative splicing) mechanisms result in accumulation of non-coding region in genome.
• Transposable elements also contain some sequences that are duplicated on integration, resulting in repeats.