I have been told that the "asterisk" in the Haplogroup 12A1* means it doesn't move down stream? What exactly does that mean in layman's terms?
From the 23andMe website:
Sometimes there are a few lineages that don't fit into any subgroup of a haplogroup. Since there isn't a mutation that links these lineages, they don't get their own subgroup. Instead, these lineages are given the main haplogroup label plus a star (*) to indicate that they are part of the main haplogroup but don't fit into any of the known subgroups
So there are defined subgroups for I2A1 (I2A1A and I2A1B) for which more information is available, but you dont fit into any of them.
What "doesn't move down stream" means, I have no idea.