How can I tweak villager breeding?

Normally in the game, the resulting baby villager and its type (savanna, swamp, etc.) is dependent on the biome the villager is in, with only a small chance to inherit one of its parents' type, if different to the biome. How would I go about changing this so that the baby doesn't spawn with it's type dependent on the biome at all but instead only inheriting one of its parents' types instead.