What would happen if a planet is removed from the solar system? More exactly what would to happen to us/Earth in general if any of the gas giants is removed by magic from the solar system ?

How long would it take after such change before we notice it ?

How major and would life resist to it ?

EDIT

For instance if Saturn or Jupiter is removed, what would happen ?
This question isn't really very clear or practical. You need to add quite a bit of information, eg which planet? 


If Sedna vanished, it would be detectable by instruments, but we would not notice. 
Jupiter or Mars might make a bigger difference. We could spot it straight away by the naked eye. 


Of course Earth life would be fine at first (unless it was Earth that was removed ...) but the orbits of asteroids and other bodies may be perturbed, which could lead to an influx of asteroid strikes - potentially - in the longer term.