The problem was that the details on Sir Paul's birth certificate did not carry the names of his parents. He applied for a fuller version of the birth certificate from Britain's General Register Office. He was not prepared for what was returned.
"The name of my mother given on the certificate was the name of the person I thought was my sister and the space for my father's name was just a dash. No father," said Sir Paul.
There was no escaping the irony: here was one of the country's most eminent geneticists and he couldn't even be sure of his own genetic identity. His parents were his grandparents, and they had brought him up as their own. Could it have been to protect their daughter, his "sister", from some scandal?
His "parents" now became his grandparents, brothers became uncles, nephews and nieces became half-brothers and sisters.
"I am not a bad geneticist," he says, "and my own family managed to keep my genetic secrets for over half a century."
You can read more in the Telegraph at http://www.telegraph.co.uk/science/7607690/Sir-Paul-Nurse-Geneticist-inherits-a-mystery.html