I know that silent mutations are neutral because they dont affect function of the protein/gene, and a missense mutation would. But lets say both occur on a neutral portion, could one or the other become deleterious? I remember my prof stating that a mutation can become deleterious if on a neutral portion. I just dont remember what would cause this.



Of course. There are tons of ways this could happen. A trivial example:

CTA codon encodes leucine.

CTA --> TTA mutation will still encode leucine.

CTA --> CTT mutation also still encodes leucine.

By your definition, each of these mutations is "silent" or "neutral" independently.

However, if you combine both mutations, they lead to a TTT codon, which encodes phenylalanine aka missense mutation.

The fancy name for this kind of genetic interaction is "epistasis". THere are many other ways in which this kind of theoretically neutral mutation becomes non-neutral, but this illustrates it simply.


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