can someone please explain how do I do this, I’ve watched countless YouTube videos and have replicated exactly what’s in the video. But I just can’t manage to stack them.

For example: I currently have two sabers Mom and Dad both had 435.6% Melee and level 191, the son comes out with 445.0% Melee, level 193, and it says 1/20 patrilineal mutations. So, I then take Son 1M and replace Dad and start breeding with the other female sabers. But I can never get it to stack, I always just get the mutated stat I initially had just moved on to the baby. I know getting a mutation is rare to begin with, am i missing something?

Any tips would be helpful