Guardian angel

...It turns out that after 4 billion years DNA can do a pretty good job of repairing itself. There's one gene in particular called the P53 gene, sometimes called the guardian of the genome, which looks for DNA damage wherever it can...

It's like a guardian angel embedded in our genes...and there are a lot of different ways DNA can get messed up...[and] when one of the two strands of DNA gets damaged this P53 gene it whistles over certain handyman proteins which come over cut the strand out... and pop in a new one because you know if you've got A and C on one side you need T and G on the other.

...other times both strands [of DNA] get snapped and that is an emergency for your body. When that happens this little guardian gene will force the cell to commit suicide because that cell will turn cancerous.

-- from Double Blasted at WNYC Radiolab, which tells the story of Tsutomu Yamaguchi, who survived both the Hiroshima and Nagasaki blasts, fathered two children and lived to the age of 95.