[furball4paws]

"I know there is a mechanism called "back mutations" which can restore lost information such as your hypothetical gene 451. What I don't know is the rate at which such mutations occur. Any idea?"

It depends on what kind of mutation it was. A frame shift or base pair substitution could back mutate at frequencies as high as 10^-4 (more typically 10^-6 - 10^-7). If it's a deletion mutation, it ain't going to happen, ever, without the introduction of extra DNA from an outside source.

[Southack]

"If it's a deletion mutation, it ain't going to happen, ever, without the introduction of extra DNA from an outside source."

Ding! Ding! Ding! We have a winner!