Cats
The slower the migration of cells, the less colour there will be. It also explained why the back
and the tail may be coloured in an otherwise all white cat - those areas are closest to the
neural crest and the pigment cells didn't have to migrate very far.
Another theory involved either of two cellular mechanisms in white spotting that "turned off"
pigment. One mechanism was apoptosis (programmed cell death) reducing the melanoblast
(pigment granule) population. In other words, the colour cells migrate over the whole surface
of the embryo, but then selectively die out. The other cellular mechanism involved
intracellular chemical communication whereby colour cells are biochemically turned off in
certain areas. Both of these suggest a chemical gradient so that cells at the extremities tend to
be first affected and stop producing colour.
annaabi.ee 
