Subject: Do identical twins REALLY have identical DNA?

I am a high school science teacher.  A colleague and I disagree on 
how identical the DNA of identical twins really is.  I realize that 
the DNA is identical, but my colleague says not necessarily.

Our high school science book says, "Barring mutations, identical 
twins have exactly the same genes."

I interpret this as saying that yes, identical twins DO have 
identical DNA.  My colleague believes that identical twins can never 
have identical DNA because there will always be mutations.

This question came about when we were reviewing questions for the 
state high school graduation test.  We would like to know the correct 
answer to tell our students.

I have researched your material and all of your information says that 
the DNA is identical.  I do feel, however, that he could have a valid 
point.  Could you please settle this for us?

Thank you for your time.
Angela Brock

Re: Do identical twins REALLY have identical DNA?