[Southack]

"The odds of the mutation appearing in subsequent offspring? The "expected value" is 100%..."

Is it really 100%?

No, it is not.

[edsheppa]

Although Dan phrased it inartfully by speaking of the expected value of the odds being 100% (odds don't have an expectation, they are one), you are being ungenerous in your interpretation. Isn't it clear that he means that in a fixed sized population each instance of a mutation will be passed on to one offspring on average? That seems intuitively obvious.