I remember being taught that "silent" mutations (when a letter in the DNA code changes but doesn't result in any change to the resulting protein) were largely neutral to fitness. A new study using yeast in Nature finds that most of these changes are actually harmful to fitness! Yeasts that were synthesized to include silent mutations reproduced more slowly in 75% of the cases. https://phys.org/news/2022-06-silent-genetic-mutations-neutral-broad.html
@dantheclamman hmm. I haven't read the article, but I would guess that different availability of the components for each of the bases would have an effect, though I don't know how large of an effect. also, the different bases have somewhat different electrical properties which is why they pair with one base vs another and why they form certain secondary structures and not others. I think it would be more surprising if there were no differences from "synonymous" mutations
