A mutation is a small permanent change in an organism’s DNA.
Can be a change in the amount of or arrangement of genetic material.
Explain why mutations are the ultimate source of variation.
Okay, so it may help to have a bit of background here. The helpful QCAA doesn’t require it, but I think it’s really useful to have this knowledge. I’m always asked “how”, because you know that A binds with T and C binds with G, so why would things go wrong?
Cause 1: Problems with DNA replication
Every time a human cell divides and its DNA replicates, it has to copy and transmit the exact same sequence of 3 billion nucleotides to its daughter cells. While most DNA replicates normally, mistakes do happen, with polymerase enzymes sometimes inserting the wrong nucleotide or too many or too few nucleotides into a sequence. Fortunately, most of these mistakes are fixed through various DNA repair processes. Repair enzymes recognise structural imperfections between improperly paired nucleotides, cutting out the wrong ones and putting the right ones in their place. But some replication errors make it past these mechanisms, thus becoming permanent mutations.
Why does this happen?
The bases that make up DNA exist in two forms. The normo A-T, C-G version, and a rare tautomeric version (where the protons occupy different positions). Some scientists think that when a base is found in its tautomeric form, it can mispair. BUT…evidence is sparse for this.
So what else may be going on? A ‘wobble’! This is basically a slight shift in position of the nucleotides in space, causing a mispairing.