I read a long time ago, I think in Scientific American, that there are two different genes involved here: one that causes your pee to have that distinct asparagus smell or not, and a different gene that determines whether you can smell that particular aroma or not.

So the article divided people into four groups: smelly smellers, smelly non-smellers, non-smelly smellers, and non-smelly non-smellers.

I don't seem to be finding the original article, but here is a related one:

https://www.abc.net.au/science/articles/2011/04/12/3189034.h...