quote:The tRNAs needed to translate GGA to glycine or GGU to glycine exist in differing quantities; altering the code can alter the expression rate of proteins.
This is correct - and there is evidence from sequence studies that certain codons are selected over others that code for the same amino acid. So these changes are not invisible to selection.
quote:This may already have been answered a dozen times over, but isn't it the case that apparently neutral mutations that have been carried along in the genome for whatever reason can then capitalize on additional mutations that have beneficial effects but that might otherwise not have been possible? Actually, isn't that what you're already saying here?
I think this is what Lenski's experiments with E coli demonstrate. I'm ready to be corrected on this though!