You could google the hunger winter in the Netherlands and the subsequent rise of diabetes in people who were hit by starvation mode while they were at just the right time of their mothers pregnancy with.
Meaning, it is not just genes, but genes, environment and the inheritance of "learned" traits i.e. epigenetics and never shall those be untangled.
You could say, well, but, behavior to which I would reply, yeah well, genes, the environment and whatnot forms behavior too.
Finally, if some tells you that they have found A or THE gene for something or other, put your brain into ignore mode so that their sloppy thinking may not soil the purity of your well ordered intellectual universe.
Unless of course your mind looks like the average garage, then just put in on a shelf somewhere.