At 02:52 PM 1/19/99 -0800, Deb Beutler wrote:

> There are three degrees of albinism. Partial albinism, as you noted, is
>an inability to make pigment in only a few locations. <snip> Incomplete
albinism
>occurs when an animal can't make one pigment but can make the other
>pigments. <snip> Total albinism is the form most people are familiar
with. It
>involves an inability to make any pigment at all. So, for bird's feathers
>and mammal hair, that means white. For eyes, they are pink.
><snip>

>what the heck does "pied" mean? Black and white? Black and some other
>color? I don't know but it doesn't mean much to me.

The term "pied" or "piebald" usually means white and some other (dark)
color. It derives from "pica", the Latin word for a magpie (there's that
"pie" word again). If ornithologists are not confused by the terms
"partial" and "incomplete" albinism meaning very different things, I have
no quarrel, but to a geneticist the term "pied" implies something fairly
specific and different from "true" albinism.
The pigment cells in mammals, and I presume in birds, are formed along the
neural crest during development and migrate outward to cover the body. The
eyes are the exception - they make their own set of pigment cells in
addition to getting a set from the neural crest. There are many mutations
that can interfere with the migration process or cause some of the pigment
cells to die, and these result in failure of the pigment cells to reach
some regions (usually the farthest from the spinal cord), giving a pied
pattern. Examples are dalmations, the white in Calico cats (the black vs.
orange is a different process), Holstein cows, etc. These "pied", "piebald"
or "spotting" mutations can cause completely white animals if all the
migrating pigment cells die off, although the eyes are usually blue, not
red, because the eye-specific set of pigment cells are usually not
affected. Most cases of what Deb calls partial albinism are probably
mutations of this type, although, as she points out, there might be
epigenetic or non-genetic causes for pigment loss.
Mutations in a completely different set of genes are responsible for
"true" albinism - the genes encoding the enzymes for pigment production.
This class would include what Deb calls complete and incomplete albinism.
In mammals these mutations affect all pigment cells (hence giving pink
eyes) because all pigment cells use the same enzymes. Besides pink-eyed
mice and bunnies, other examples include Siamese cats, in which the
pigment-forming enzyme is temperature-sensitive and can only form pigment
at the extremities where the body temperature is cooler (a type of
incomplete albinism).
There are also genes that control pigment production in particular regions
to generate pattern elements. An example is tabby striping in cats.
In mammals, the main pigments are melanin (black) and phaeomelanin (brown
or yellow). Birds have these pigments and also get caretenoid (yellow,
orange, red) pigments out of their diets, and can lose these latter
pigments if their diet does not supply them. In addition, they have
structural colors (blues and greens) that are caused by diffraction over a
pigmented backgound.
Aviculturalists presumably use "pied" because they breed birds and are
familiar with heritable pied mutations, of which there are many.
Ornithologists such as Deb may prefer not to prejudge the reason for
pigment loss, since they may not be able to follow its inheritance in the
field, or may encounter dietary loss of pigments.
I would add, however, that if pigment is missing from only from one area
of a pattern (as opposed to a whole color or pattern element being absent)
particularly on the ventral side, in my judgement it is quite likely to be
due to a pied mutation. The mutant/hybrid mallard drakes (hybridized to
mutant domestic ducks?) that I have seen at Seward Park and Green Lake that
have white patches on their fronts (ventral) are examples of birds that I
would suspect have a pied mutation, although the region affected nearly
corresponds to the brown front patch and could be in a gene controlling
that pattern element (I'll have to look at the ducks more closely).
Deborah's house finch with white spots on its cheeks and above its upper
mandible (both near the ventral midline) also sounds like a pied mutation.
I would be quite surprised if these white patches had a non-genetic cause.
One clue for telling pied vs. pattern mutations is that pied mutations are
likely to be at least somewhat asymmetrical, while pattern mutations are
likely to be symmetrical.

Keep reporting those variants,

Paul Talbert