The tracks indicated by a "ball" logo
have been lifted from a previous assembly of the same organism
with a minimum of quality-control scrutiny (e.g., have been lifted
from hg17 or hg18 to a later human assembly). The number indicated
on the logo indicates the version of the assembly that the track
was lifted from. These tracks are provided to our users with the intent
that they assist in interpretation of other data, but must be used
with caution. Not all annotations remain intact when lifted in this
manner and in any case, cannot by definition contain any sequence
that is new to the newer assembly.
It should also be noted that tracks containing large regions will
lift less well because of the increased chance of spanning a region
that changed between the two assemblies.