>>...And many of those gene variations won’t be apparent until long after breeding age.
That presents an interesting puzzle. Take the APOe4 variant; there's some evidence that as recently as a couple of thousand years ago it was the most prevalent variant - which makes sense as it provides come survival benefits, notably an immune system better at fighting off parasites and bacterial infections (that latter meant women were more likely to survive childbirth). It also has the downside of a larger risk of Alzheimer’s - for people past 65, well past 'breeding age'. Humans got to understanding sanitation and so reducing parasitic load and bacterial infection relatively recently - and the discovery of antibiotics is pretty much 'last week' in evolutionary time. In spite of that, the most common variant is now APOe3 (lower risk for AD, but higher for parasitic load and infection).
I'm wondering how we got here. Even the 'grandmother effect' doesn't seem to explain it.