When you have a trait that can assume different values (height, IQ etc.), and you have x heritability, you can say that x% of the variance between individuals is explained by genes.
But let’s consider bipolar disorder. In this case it can be present or not. Let’s say it has a heritability of 70%; how do you interpret this value?
In: Biology
I feel like you’re trying to model something with direct math that is not nearly so simple as you are making it out to be. Disorders are generally not some specific % heritability, since there are many factors that come into play not only in how they come into effect, but when and how severe. Even things that have discrete values to can measure such as height/IQ (putting aside how quantitative and trustworthy these measures are), they are a complex outcome from a multitude of interacting factors.
You can look at possible genetic components to disorders, but you will frequently be looking at something that is always at least partially a black box. Certain things linked to disorders might depend on environmental triggers, age, *other* genes, and a number of other factors before they actually come into effect or how badly.
You can 100% inherit genes linked to a disorder and *not suffer from it* if these other factors or genes required for it are not there. And if you say, have 3 genes, 4 epigenetic triggers, 1 age-associate decline (gradient not binary), you can’t get a % inheritance off of that, especially when if, say, 2 other genes can makeup for 1 of the 3 core genes, you might have different combinations of epigenetic triggers that yield the same effect, and so on.
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