Function is a property of tertiary structure, which you do not know.

Structure determines function but you do not know if structure is altered in a way that inhibits/enhances function. Strictly speaking, benign missense mutation do exist.

Of course if your professor told you otherwise, I’d stick with his/her story.

In addition to the two point mutations–which may or may not have an effect on function–is the mutant also a frameshift mutation? If it is, then, unless there is a nearby reversion back to the correct reading frame, then the mutant is very likely non-functional. But that’s only IF the dropped G is meant to indicate a frameshift. You need to see the wild-type and mutant sequences farther to the right to tell.

This may be a made up sequence—not that it matters. Nine residues isn’t much to go on, but Blasting the native sequence didn’t pull out anything at all. I didn’t check your translation, so if that’s in error, then so was the Blast target.

I can always be wrong, but I don’t think dominant/recessive or homozygous/heterozygous was meant to be considered. My best guess is that the question you are to answer is whether or not the mutant chain would be functional in any sense; if this were an alpha-globin, could it team up with beta-globin to yield a functional hemoglobin molecule, say? There are three base changes near the Met introducing two amino acid changes in the mutant relative to the wild type protein. But you can’t say much about function from that—the mutant polypeptide may or may not be functional. I don’t know for sure what was intended by dropping the final G. It would have been nice if they had given you more of the sequence to the right of what we see so we can tell if there really is a frameshift or not. You can’t even say what the ninth residue of the mutant protein is without that information. My answer, to be honest, is that there is insufficient information to make a reasonable prediction. If the dropping of the final G was intended to indicate a frameshift, then most likely the mutant chain is non-functional. But they should have given you more ot the sequence if that’s what they had in mind. You really can’t tell from the information you’ve been given, unless you have information you haven’t divulged.