I believe you pass on some sensibility in that area, like the kids will be more prone to get the disease, not that they will actually develop it. Major influence if both parents have it, even more if their parents had it.

For example, if your grandparents had lung cancer, your parents have lung cancer, it would be wise if you didn't smoke or inhale toxic chemicals on a regular basis.

Edit for clarification: by inhaling toxic chemicals on a regular basis I mean work in places where said chemicals are present: factories, paint shops, gas stations etc

Bit long, but I explained this to my 5yo and they got it.

I think a more appropriate word for "a lot" is "often".

DNA is mostly information about how the cells work and how stuff is made in our body (this is how we share 70% of our DNA with cucumbers and 90 something % with rats).

Only a very small percentage is related to aspect (human vs ape for example), less for geographical features (caucasian vs african for example) and even less for individual features (Bob vs Mike). Our genes suffer constant mutations over our lifetime (this is how evolution works, btw), but only a distinct few can "survive" and change something.

Think of yourself: your cells work the same way as they always did, so the big part of your DNA didn't change. You still look human with aging, albeit with minor changes in appearance (but that is due to other factors), so that part didn't really change. So while mutations occur often, they don't really change that much DNA.

Any time a mutation occurs, it alters what was already there, it doesn' create something new. A good analogy is with BMW and payable options: they are there but just need to be activated (and sometimes, when they activate, something goes wrong and your blinkers blink blue).

Between extreme causes of mutation you can find autoimmune diseases and cancer

That's a nice paradox: if it was spawned there, its offsprings will return. Sadly, the cycle will end then, between the blades of the impellers.

If it had passed through the blades unharmed, maybe more will come to spawn there, repeating the cycle and creating more impeller resistant and junk eating eels that would mutate and fight the ninja turtles