Growing avacado from a seed

Question

My mother in law said she planted an avocado seed and a grapefruit tree grew from it.

How is this possible?

Thanks

Answer 1

This is entirely impossible. More than likely a seed from another tree was present in the soil. Even if it were a grapfruit, they will revert back to a parent. In most cases it will not be a grapefruit, or even edible.

I believe the tree to have a mistaken identity. If you can post pictures, I can see if maybe we can help identify it for you.

Answer 2

Thanks I don't need to post a pic. I told them the same thing that it wasn't possible and it started leading to an argument so I just dropped it and asked you.
I was told that it wasn't possible to grow Avocado trees in Northern California Zone 9 because they are grafted onto a different root stock with scions. Is that true?
Thanks