>The way the Pokémon inherits moves are based solely upon the base form's own learnset. The parents that need to know the moves are as follows;
Moves in baby's Level Up: Both Parents
TM Moves: Father (pre-XY)
Egg Moves: Father
Move Tutor Moves: Cannot be bred
The Gyarados must know Twister in order to pass it down to the offspring.
In X/Y the mother can also pass down egg moves.
>As of Pokémon X & Y, it's now also possible for the mother to pass Egg Moves down. If the mother has one of the Egg Moves of the baby, it will pass the move down.
Hope I helped.