Why do some health conditions skip generations?
If my grandad (fathers side) died of stroke and my other grandad (mothers side) died of lung cancer does that put me at equal risk in having those problems as my mother & father?
Why do genes skip generations?
In: Biology
Genes do not skip generations. Their effect might.
It’s all about risk. Say your grandfather had a gene that made them more likely to have a stroke. Maybe your dad did too. Just because he did not end up having a stroke doesn’t mean he was not genetically more likely to have one.
Additionally the expression of the gene may also be completely hidden, not only because of lifestyle, but also because of some other gene that “override” the first one. The simplest example of that is for recessive traits. Blood type is a common example because it’s a trait that mostly just depends on a single gene (most traits are much more complex, but the simple case is enough for you question). For each gene, we all have two copies. Say my both of my parents have the gene for blood type A, and that for O. As a result, that will both be type A (O is recessive, so if you have both O and A versions, you’re A). And yet I could still be O, if I get the O version from each of them. So the O skipped a generation, simply because at my parent’s generation it was “hidden” by the A.
> does that put me at equal risk in having those problems as my mother & father?
No. From the information available, your parents have a higher risk than you. You have 4 grandparents. All together, that’s 8 versions of each gene. But from those 8, you only inherit 2. We cannot know which versions you got, but if any version of a gene from your grandparent give a higher risk of stroke or cancer, there is still only a 25% chance you even got that version. Meanwhile, your father has 50% chance of inheriting each gene version from your grandad.
Lastly, keep in mind that your grandad having a stroke, or your other grandad having a lung cancer, might have nothing to do with a particular genetic risk at all. It’s possible, sure, but even that is far from certain.
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