At which point does an egg of non-chicken become an egg of chicken?

Is a “chicken egg” an egg laid by a chicken, or an egg that will hatch into a chicken?

It’s an egg that will hatch into a chicken, since the “first” chicken must have hatched out of an egg that was laid and fertilized by two “non-chickens” whose DNA combined together to make a full-blown chicken. Of course it wasn’t actually just one egg, but really, no matter how you think about it, the egg came first.

Can mutations that occurred during life be transmitted to offspring? Biology classes were a long time ago.