Notch
Asymmetric Expression for Nothch/Delta/Serrate is associated with the Anterior-Posterior Axis of feather buds.
Notch-1, Serrate-1 and Delta-1 are not expressed when feather primordium is set.
They are rather involved later when the anterior - posterior axis is set. These molecules and BrdU labeling are preferentially expressed in the posterior feather buds.