So you’ve been given the ultimate choice, what do you do? This guide for South Park The Fractured But Whole Collect DNA From Mom Or Dad? will tell you what happens when you decide to harvest DNA from your mom or your dad. While the quest choice is whether you get your moms or your dads DNA, the choice is a little more sinister. Do you kill your mom or your dad? Whatever you decide, only one of them is making it out alive.
During the later parts of the story you find yourself exploring Mephesto’s Genetics Lab. Towards the end of the area you discover your mom and dad, both injured inside a lab. Your mom asks you to kill your dad and your dad asks you to get your moms arm and use her DNA. Below is the outcome of both choices.
The game gives the impression that this is quite a vital choice, something that will impact later stages of the game. However, despite playing through to the end on both outcomes, I was unable to differentiate between the two choices.
So really, it’s up to you whether you kill your dad or kill your mom.