What is the definition of a mutation?

Question

There are two alleles that determine the sensitivity of a person to Coumadin (a medicine for blood thinners used to treat a stroke etc). Sometimes you encounter the terminology that one has a *mutation* on both alleles (father's and mother's side). But why is that called a mutation and not just a *variation*? Does a mutation mean that it *changed during lifetime*, or is the difference between mutation and variation arbitrarily defined? Or is there really a kind of standard taken where deviations are considered to be mutations?

Answer 1

This is a good question. Technically, any change in a gene's DNA sequence is a mutation, from the Latin word mutare, to change - or a variant, since the sequence varies. In practice, some people started using "mutation" for harmful changes. Nowadays, a genetic testing lab will classify a variant as pathogenic or likely pathogenic, rather than calling these variants mutations. The genetic responses to Coumadin are most likely inherited from the parents and found in all of the person's cells. They are far less likely to be a new mutation in that person. It is possible, but less frequent.