On Mon, 21 Oct 1996, Cynewulf wrote:

	I've noticed in a bunch of fanfics that Genma is often called 
'Uncle Saotome' by the Tendo sisters.  I was just wondering why.  Is it 
something in the japanese original I never noticed?  Or just creative 
license?

That's because in Japanese they refer to him as Ojisan, which translates
most conveniently as Uncle Saotome. 

As a side note, in Japanese, people tend to refer to non-family members
as if they were related - i.e. calling older boys/girls as
oniisan, oneesan, and adult men and women as ojisan, and obasan.