You could have a secret twin (but not the way you think) - Kayla Mandel Sheets

While searching for a kidney donor, Karen Keegan stumbled upon a mystery. After undergoing genetic testing, it turned out that some of her cells had a completely different set of genes from the others. And this second set of genes belonged to her twin sister who had never been born. How did this…

Source: TED-Ed (2021-09-16)