Dalek factor

The Dalek Factor is a genetic trait that was added to the Humans by the Daleks.

Toward the end of the Last Great Time War the Daleks sent a time capsule to 70 AD Earth in order to spread the Dalek Factor amongst the Humans. The capsule's engine exploded, and the Dalek was killed soon after impact. It was only able to release a small amount of the Dalek Factor, leading to only 1 in 500,000,000 Humans having it. The only known carrier of the Dalek Factor was Kate Yates.

The Dalek Factor is generally hidden amongst the genes. When the casing of the Dalek was rediscovered and activated in the early 2000s, the Dalek Factor in Kate was reactivated. When Kate Yates was hit by a car, she was able to survive and regenerated the damage. Her hair turned blond and she started gaining immense intelligence and increased strength. She also started to develop a Dalek mindset, hating all other Humans and trying to help the Dalek. When she touched the Dalek casing she was also able to reactivate it, causing a new Dalek to be grown from raw materials in the case. Eventually, she was able to overcome her Dalek instincts and was able to help the Doctor and Rose kill the Dalek, causing her Dalek Factor to deactivate. (TDA: I Am a Dalek)