How do the bloodline traits work?

When a spellcaster without a bloodline trait gets a child, the child recieves the weak bloodline trait. When a spellcaster with a weak bloodline trait has a child, the child will get a strong bloodline. And a spellcaster parent with a strong bloodline will lead to a child with an ancient bloodline. I don't have many spellcasters with children, the few I had always had a spellcaster child. But I think the bloodline is independent of the occult state of the sim. As far as I know both human sims and spellcasters sims can have a bloodline trait but the trait only does something for the spellcaster. The bloodline trait determines how easy a spellcaster can learn magic. The human sim doesn't get any advantage, unless he decides to become a spellcaster.