Question: Why do they have the extra unnecessary information if they're just going to get rid of it?

Judith Sleeman answered on 19 Jun 2012:

The messenger RNAs from the genes, you mean? That is a really good question, as it seems bonkers for the cell to put all that energy into making RNA that it doesn’t need. There are (at least!) a couple of reasons, though.

Firstly, it means that the cell can make a whole lot of different (but related) proteins from the same original DNA sequence by putting together different combinations of exons (the bits of the RNA that carry the sequence needed for the protein). This happens with a muscle protein called myosin that needs to be slightly different in heart muscle and in skeletal muscle.

Secondly, looking at evolution, it means that there is more opportunity for new proteins to be made (say if a mutation happens that means the RNA is spliced differently, so the animal has a different version of the protein) so splicing is thought to have lead to more complex animals.

Thirdly, we are starting to find out that much of the RNA that is cut from the gene and not used to make protein isn’t just thrown away. It’s really important for regulating gene expression: for making sure the cell makes enough of the right kinds of proteins. So, the more new things we learn, the more the old stuff starts to make sense. One of my favourite things about science!

Actually, that was already more than ‘a couple’ of reasons, wasn’t it!!