Will my Minecraft 1.1 world ever contain a Jungle biome?

Question

Now that Minecraft 1.2 has been released, I'm wondering how much of the new stuff added will ever appear in the world that I started playing in 1.1. Specifically, a new Jungle biome has been added, and the wiki page says this:

Jungles will only generate in chunks generated after 1.2.1.

I'm not sure how to interpret this. If I walk far enough in my world I started in 1.1 to a chunk I've never visited before, does it have a chance of being a Jungle biome? I guess what I'm generally asking is if the biome of a chunk is determined when the world is generated, or when the chunk is first visited?

Answer 1

Yes. If you move outside the areas you have previously visited, the new biome type will have a chance of showing up.

Confirmed this in both singleplayer and multiplayer.

Answer 2

Yes. If you visit a chunk that's never been generated before, and using the new world generator that chunk would be jungle, it will be jungle.

Note that you'll get hard edges between old and new chunks, where the terrain doesn't match up.