Mutations Affect Evolution

A DNA molecule with a mutation. Getty/Marciej Frolow

A mutation is defined as any change in the Deoxyribonucleic Acid (DNA) sequence of an organism. These changes may happen spontaneously if there is a mistake when copying the DNA, or if the DNA sequence comes into contact with some sort of mutagen.  Mutagens can be anything from x-ray radiation to chemicals.  

The overall affect a mutation will have on the individual depends on a few things.  In fact, it could have one of three outcomes.

 It could be a positive change, it could impact the individual negatively, or it can have no effect at all.  The harmful mutations are called deleterious and may cause serious problems.  Deleterious mutations may be a form of the gene that is selected against by natural selection, causing the individual trouble as it tries to survive in its environment.  Mutations with no effect are called neutral mutations.  These either happen in a part of the DNA that is not transcribed or translated into proteins, or it is possible the change occurs in a redundant sequence of DNA.  Most amino acids, which are coded for by the DNA, have several different sequences that code for them.  If the mutation happens in one nucleotide base pair that still codes for that same amino acid, then it is a neutral mutation and will not affect the organism.  Positive changes in the DNA sequence are called beneficial mutations.

 The code for a new structure or function that will help the organism in some way.

The interesting thing about mutations is that even if at first it is a deleterious mutation, if the environment changes these normally harmful changes can become beneficial mutations.  The opposite is true for beneficial mutations.

 Depending on the environment and how it changes, beneficial mutations may then become deleterious.  Neutral mutations can also change to a different kind of mutation.  Some changes in the environment necessitate the beginning of reading DNA sequences that were previously untouched and using the genes they code for.  This could then change a neutral mutation into either a deleterious or beneficial mutation.

The deleterious and beneficial mutations will affect evolution.  Deleterious mutations that are harmful to individuals will often cause them to die before they are able to reproduce and pass those traits down to their offspring.  This will shrink the gene pool and traits will theoretically disappear over several generations.  On the other hand, beneficial mutations could possibly cause new structures or functions to arise that help that individual to survive.  Natural selection would rule in favor of these beneficial traits so they will be the characteristics passed down and available to the next generation.