In biology, a mutation is a change in the genetic material. This means changes to the DNA or to the chromosomes which carry the DNA. All such changes are heritable (can be passed on to the next generation) unless they have lethal effects.
Mutations can happen for several reasons. It can happen because of errors when meiosis produces the gametes (eggs & sperms). Damage by radiation, or by certain chemicals may cause mutations, but they do occur occasionally at random.
Types of mutation
When DNA is copied mistakes are sometimes made – these are called mutations. There are four main types of mutations:
- Deletion, where one or more bases are left out.
- Insertion, where one or more extra base is put in.
- Substitution, where one or more bases are substituted for another base in the sequence.
- Duplication, where whole genes are duplicated.
These terms are explained in the third diagram.
- Deletion: a piece of chromosome is lost, together with any genes which may be on it.
- Duplication: part of a chromosome is repeated
- Inversion: part of a chromosome is reversed end to end
- Insertion: a smaller chromosome is inserted into a longer chromosome
- Translocation: part of a chromosome gets moved onto another chromosome
Consequences of mutation
Mutations may be bad for the organism, or neutral, or of benefit. Sometimes mutations are fatal for the organism – the protein made by the 'new' DNA does not work at all, and this causes the embryo to die. On the other hand, evolution is moved forward by mutations, when the new version of the protein works better for the organism.
Mutations are the ultimate source of variation, upon which natural selection acts. What happens is that some mutations affect the organism's ability to live and reproduce. This is an important part of the theory of evolution. The amount of heritable variation carried by a population can be huge, and as a consequence natural populations have the capacity to change and adapt to conditions in their environment.
- Maynard Smith, John 1998. Evolutionary genetics, 2nd ed. Oxford. p53–64