miR family - (Sep/22/2009 )

Please help with the following questions:
What is exactly the definition of miR family? Does it mean: a group of different miRNA genes from which mature miRs with the same sequence (up to 2 mismatches) are produced?
What about overlapping miRs from the same miRNA gene?
If I have a long list of miRs, how can I devide them into family groups?

Many thanks,
root

If 2+ miRNAs have the same seed sequence (nt 2-8) then they are part of the same family, i.e. miR-15 and miR-16. Additionally, if there are 2 miRNAs very similar with only 1 or 2 nt differences, they are named with a letter after the number, i.e. miR-15a and miR-15b.