Which Pokémon games introduced breeding as a gameplay mechanic?

Pokémon Gold and Silver introduced breeding as a gameplay mechanic.

In these Game Boy Color games, compatible Pokémon left at a Pokémon Day Care can produce an Egg. The Egg eventually hatches into a young Pokémon, adding a new way to obtain and develop team members.

Breeding also introduced inheritance rules. The offspring generally belongs to the mother’s species, while some moves can be passed down from the father. Ditto provides a special exception because it can breed with many Pokémon outside the No Eggs Discovered group.

The feature expanded the series beyond catching wild Pokémon. It became important for obtaining Baby Pokémon, passing down moves, and later refining traits for competitive battling.