DNA mutates. Not like in X-Men, but in tiny, boring ways.
Sometimes a child inherits a new bit of DNA that neither parent has. The test sees this and goes, “Huh? Who are you?”
Labs know this trick. They test multiple markers. But if a rare mutation pops up at exactly the wrong spot? The result can look like a mismatch.
The “Sample Swap” Story
Here’s a real-life, juicy example: A man sends in a cheek swab. The lab says he’s not the father.
He’s devastated. Six months later, he gets a mysterious letter: “Oops, we swapped your sample with a guy named Steve.”
This actually happened. Human error is the ultimate plot twist.
