[thedoc (OP)]

Angelo Odato asked the Naked Scientists:
   Our cells divide billions of times over our lifetime.  Mutations occur at some frequency.  If any of these mutations persist, couldn't parts of our body have a different genome than another?
What do you think?

[evan_au]

couldn't parts of our body have a different genome than another?

Yes. When DNA is copied as a cell divides, there is a chance that a DNA base will be misread (substituted for another), deleted, or an extra base pair inserted. This rate is estimated as 1 in 10⁸ base pairs.

Humans have "proofreading" steps in DNA replication that can detect and correct most of these errors. This leads to an average of around 0.2 to 1 mutation every time a human cell divides.

This includes "natural" radiation and chemicals in food. Additional mutations can come from exposure to carcinogens like cigarette smoke or nuclear explosions.

Human cells can divide up to 70 times, meaning that each cell of your body can accumulate up to 70 mutations during a lifetime - although most of these divisions occur in growth from an egg cell to a newborn. Cells from very different parts of the body (eg skin & gut, head and feet) derive from different parts of the embryo, they are likely to have very different sets of mutations.

Mitochondria DNA has a higher mutation rate than nuclear DNA: around 1 in 10⁵ base pairs (but this is counterbalanced by the smaller mitochondrial genome).

This is why "identical twins" are not entirely identical.
See:
http://book.bionumbers.org/what-is-the-mutation-rate-during-genome-replication/
https://en.wikipedia.org/wiki/Mutation_rate