I guess I don't know what you're saying here. A bolus of mutagenic radiation impacts a DNA base and modifies the genetic code, or maybe there is a copying error, and the genome is slightly modified. Is that the process that you are suggesting can go awry?
What can go awry is the development of offspring if that mutation occurred in an egg or sperm cell. The mutation might cause death, disease, or disability. It's the process of constructing this offspring that goes awry when this happens.
Or, there might be no effect. Many amino acids have more than one codon (in case you've forgotten, that's a three-base group on the DNA that corresponds to a "negative" set of three bases on a piece of transfer RNA called an anti-codon connected to an amino acid). Here's a corner of the table of all possible anticodons (4^3=64) for the tRNA. Look at phenylalanine (Phe), which is coded UUU and UUC. These are nucleic acids that will bind to DNA codons AAA and AAG (also nucleic acids). Suppose the DNA mutates from AAA to AAG. That will have no effect on the protein generated by the process. Phe will remain in the same spot:
View attachment 94097
But maybe the mutation changes the amino acid coded, and there is a change in the protein generated. Maybe that protein is an enzyme, and maybe the mutation caused an inconsequential change in its overall conformation (3D shape) remote from the active catalytic site (where the chemistry occurs).
Or maybe the new enzymes is slightly more efficient. That's a beneficial mutation if it results in increased survival and reproduction in the offspring.
What can go awry is the growth and development of the conceptus, not the mutation process.
No, I wouldn't pick a fight with you. I was disagreeing your interpretation of the quote, which was that some and some and some imply 1/3 each.
Thanks, and you, too. Hope it's safe and comfortable where you live.