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No “magic gene”(r/Fantasy)
There are advantages and disadvantages to going with the “genetic magic” route. There are a lot of readers out there who enjoy the idea of a character who is born special – I’m just not one of those readers. I prefer fiction where characters have to put in a significant amount of effort in order to be powerful, both in terms of putting in work and thinking about how best to apply their abilities.
I personally tend to prefer settings where any character can learn magic to some extent, but there are limitations based on resources, education, character interest, cultural values, etc. This can be more challenging to explain in a satisfactory way than simply using the genetic approach, but ultimately I find it more satisfying.
If you don’t mind self-promotion, I think my novel Forging Divinity fits your criteria pretty well. Characters have predispositions toward specific types of sorcery from birth, but everyone has the potential to cast some kind of magic, and it’s possible for characters to develop magical for types they aren’t born with a talent for.
All three of my perspective characters are practitioners of different types of magic, and each type of magic has a unique cost. For example, sight sorcery allows the caster to create illusions or other sight-based effects, but at the cost of the caster’s eyesight.
Using a specific type of sorcery is like using a muscle; you’ll get stronger, but if you tax yourself too much, you can cause yourself permanent harm. You can build up your ability to use sorcery through non-sorcerous means (e.g. specific types of diet and exercise can help prepare your body for specific types of sorcery), and some military organizations encourage this kind of cross-training.