Except for Mendelian diseases, not really. The sad fact is that for the so-called "complex diseases", we have very little idea what is going on inside the black

Except for Mendelian diseases, not really. The sad fact is that for the so-called "complex diseases", we have very little idea what is going on inside the black box. I won't presume to guess whether we know less about them or about behavior, but the ignorance level is very high in both cases. They are called "complex" because we don't understand them, and because they seem to have many causes, both individual genetic loci and environmental variables, each contributing a little bit rather than something like sickle-cell anemia which has one big cause. However, I think our techniques are quite sufficient right now to say X% of the variance in phenotype P is attributable to genetics (i.e., genetics partially cause P). That is a totally different thing from explaining how the genotype causes the phenotype.