Single nucleotide polymorphism vs single nucleotide mutation - (Apr/15/2008 )
I'd like to ask whether these 2 words are interchangable and mean the same thing:
Single nucleotide polymorphism vs single nucleotide mutation
Thx a lot
Yes. The word polymorphism is preferred, though. It's not always possible to determine what the initial state was, so if you have a C in this allele and a T in that allele and you don't know if the C changed (mutated) to a T or the T changed to a C, then the best description of this nucleotide site is to describe it as being polymorphic. Point mutation is a term also used, but with the same limitation as above. In molecular phylogenetic studies, close relatives to the species you are working with are often used to try to determine what the ancestral state was. If the close relatives have a C, then the T is inferred to be the mutation (but without any guarantees).
There is a subtle difference between the two words, and which one you should use depends on the context.
I would have thought polymorphism is used where there is no association with disease, and mutation where such an association exists. Also, a polymorphism is probably more common than a mutation. Of course, every polymorphism had to start out somewhere as a single-point mutation, but it has survived long enough to penetrate into the general population.
Yes, there is much confusion concerning these terms. The human medical community oftens limits the term "mutation" as something that is inherently bad, causing disease. Genetically, though, the term simply means a change. Most mutations are probably neutral, causing no change in phenotype. A mutation in the third position of codons, for example, (usually) causes no change in the protein sequence. Mutations lead to polymorphisms at the sites of mutation. The term "polymorphism" simply means "many forms", and has nothing to say about good or bad.