They will work a little differently than in Muties 1.0. You won't buy them...in fact, you don't have to participate in mutations at all.
When you create a character (or upgrade to the new type, for existing characters), you'll also select your species:
Homo sapiens: A normal human with stable DNA> This species does not mutate.
Homo transitus: At the beginning, just like Homo sapiens, but with less stable DNA. As transitus is exposed to toxicity (gains levels, experiences some special events, gains large amounts of toxicity at one), he/she will pick up a random mutation.
Mutations have levels, and when a character gains a mutation it will be a random one at their level or below (no duplicates). Some will be good, some bad, and some will have no game effect at all (but be strange). Some mutations will be operable (they can be removed), but finding somebody able to do so will be difficult and expensive.
Mutations will not have "special" effects; this is, they will only affect skills and SMACK, if they actually do anything at all. A string of really bad luck could be very harmful to your character, but a string of really good luck could really pump you up. Overall, mutations so far are weighted slightly in favor of the beneficial.
I'm throwing this in because adding it will actually be very close to trivial, and I miss mutations. 