This was interesting. Jim Gaffigan’s ancestor’s original surname was Gavahan. For some reason that relative changed it to Gaffigan before he left for the US, because the ship’s manifest shows it as Gaffigan. Jim shares a segment of DNA with a distant relative of Derek Jeter, whose mother is caucasian.
Transcript is here:
https://allarts.org/programs/finding-your-roots/no-irish-need-apply/