“If you flip a base and it doesn’t make any difference, then you’ve just proved that it was junk-DNA, right?”
Not quite. Certain bases in the protein-coding sections of genes (i.e., definitely not junk DNA!) can be flipped without changing the resulting proteins. This can happen because there are 64 different codons, but only 20 different amino acids are used to build proteins, so the DNA code is not one-to-one.
It might be safer to say that if you delete the base and it makes no difference, then it was junk, but even this will run into problems...
“If you flip a base and it doesn’t make any difference, then you’ve just proved that it was junk-DNA, right?”
Not quite. Certain bases in the protein-coding sections of genes (i.e., definitely not junk DNA!) can be flipped without changing the resulting proteins. This can happen because there are 64 different codons, but only 20 different amino acids are used to build proteins, so the DNA code is not one-to-one.
It might be safer to say that if you delete the base and it makes no difference, then it was junk, but even this will run into problems...