If you breed a trillion animals, and feed them all to your snakes...mc was not spread to another generation
But that would require starting over with a completely fresh source.

Does anyone really feed off a whole colony and start fresh when their first generation breeders are old?

That's about the only way to guarantee it.

Yes, and high white is very well associated with megacolon, or rather, vice versa.

It's due to the fact that in the embryo's development, the cells that develop the nerves that control the function of the colon travel along the very same route that the pigment cells travel. When the migration of the pigment cells is halted, the nerve cells are often stopped as well. Resulting in a colon that does not function properly, or at all.

It's not just a crazy myth, it's science. When we advise to stay away from high white rats, it's not just for kicks and giggles. I have always said that not all high white rats carry the necessary genes for megacolon, and megacolon does not always show up in only high white rats, but the risk is higher due to my explanation above.

The only way to prove a line does not carry megacolon is through controlled line and inbreeding. It's very possible to do so, but most feeder breeders are not interested in genetics.