How can a DNA mutation be neutral?

The effects of a mutation can be limited at several stages of gene expression. 1) Transcription: If the mutation is in a non-coding region, this is not transcribed into mRNA and so there is no change to the amino acid sequence. 2) Translation: If a mutation involves the substitution of one base for another, it may not change the amino acid encoded by the DNA. This is because the genetic code is degenerate (several triplet codons code for same amino acid). This is a silent mutation. 3) Folding: If a mutation causes a change in the amino acid encoded by the DNA, this may not affect tertiary protein structure or shape, so it may function normally. 4) Function: If a mutation changes the protein structure, this may not give a selective advantage or disadvantage.