I guess I really shouldn't expect most role-players to be well-educated in biology. Especially when you consider the ages of most players. But still, it'd be nice if I could see some believability once in awhile...

"A scientist walks into a room where a human subject is being held in a cage. He has a needle full of some suspicious liquid. He injects the human. Suddenly, the human grows cat ears and a tail, and a pair of feathery wings sprouts from his back."

This is a typical example of what you see in this type of role-play. (It was, however, fabricated by myself.) Alas, it's extremely error-filled, outright contradicting known laws of genetics and physics.

First of all, growing new attributes in such a manner is completely erroneous. No matter what, nothing grows in a matter of seconds. Period. Also, you can't just cause things to grow without some darned good explanation.

Mutations, Natural and Induced:

Basically, a mutation is when something abruptly changes in the genetic code. For example, if a yellow flower produced white-petalled offspring, this would be a mutation. In real life, mutations are often too small to make any visible difference.

In the good old days, comic book writers such as Stan Lee used radiation as a catalyst for superpowers and mutations. The X-Men, for example, were humans whose genetics were mutated by radiation. Spider-Man was bitten by a radioactive spider. When these stories and comics were published, people didn't know as much about radiation as they do now. Nowadays, it's a well-known fact that radiation does cause mutation - in the form of cancer. This makes it an implausible catalyst.

I've seen a few GL-type RP's titled "Teens Injected With Animal DNA." To put it bluntly, injecting someone with animal DNA wouldn't do a thing. That would be about as effective as hooking your toaster up to your computer, and expecting your computer to do something with the toaster. The two are completely different, incompatible pieces of technology.

Next, nothing can grow or mutate that fast, ever.

Consider how big a chick is after it's hatched. It can fit into the palm of your hand quite comfortably. By the time the chicken is full-grown, you can hold the little beastie in two hands (providing it'll hold still). While a good deal bigger than it was before, it's certainly not exceptionally huge. And it took several months to grow up.

For anything living to grow, it must aquire energy and mass. Or, simply put, it needs to eat. The faster something grows, the more it will need to eat. Therefore, if someone suddenly began sprouting a cat tail, he or she would have to eat enough food to support it. (Once the tail was fully grown, the subject would not require as much food.)

Also, it would be impossible for anything to grow at an extremely rapid rate and form something coherent, unless it happened to be a super-intelligent organism. Cells do not happen to be super-intelligent organisms. Grow something too fast, and you'd basically end up with a mass of cancerous cells. Yeechh.

Nanites could make a plausible explanation. These microscopic robots could theoretically be programmed to do many tasks. A character could be injected with nanites programmed to give him or her specific attributes and/or make specific changes. It would still take some time (energy and mass!) but if they were, say, controlled by a supercomputer, you'd essentially have your super-intelligent organism right there.

Mutation in General

"Sylvia was a mutant. She had green skin and white, feathery wings and was telepathic..."

As you probably already know, DNA is the coding which basically tells organisms how to grow. Now, I want you to think of DNA as a poem written on a piece of paper. For whatever reason, you decide that you don't like the poem anymore... so, you toss it in the shredder.

Oops! You decide that you want the poem after all, so you fish out the shredded remains and do your best to piece them together. In your haste and panic, however, you got a few pieces out of place. The poem doesn't even make sense!

Expecting a mutation to give someone, say, wings, is like putting a poem in a shredder, putting it back together a little differently, and expecting to get a deep and meaningful poem. In actuality, you'd get nonsense!

In terms of genetics, "nonsense" translates into things like cancer, mental retardation, or faulty organs. Things like body parts not being in the exact right place, or missing altogether. Not exactly a pretty picture.

I could see someone altering the genetic code and using the new code to grow an entirely new creature. However, the DNA code isn't simple by any means, so there could possibly be several errors - errors which could, for example, cause such a creature to have a terribly short life-span due to the internal structure being too messed up, or make them deathly allergic to certain compounds.

Keep in mind that cloning and genetic manipulation is difficult and iffy with today's technology. At the moment, there's no way anybody could make a sophistocated genetically-altered creature. (In the future, however, who knows?)

Remember, it never hurts to do a bit of research. Try looking up biology and mutation (not comic book biology!) online - not only can you learn a lot this way, but you can find many interesting ideas for new characters.