It was a (dumb) joke. The phrase I used came from Shrek.

https://knowyourmeme.com/memes/some-of-you-may-die

But, to nitpicking, I guess you could say the selection came after the gene got recombined. Surviving the zap and was lucky enough to do the recombination still do nothing. The effect of the recombination, i.e. the expression of the foreign gene, is the interesting part. If it confers an advantageous trait to the mutant, that mutant get selected for in the game of life. If it doesn't, which is most often the case, it is selected against, and would be quickly removed from the genetic pool.

We do this selection quite often in the lab so perhaps it unconsciously leaked out in my phrasing.