Subject: Re: albinism
Date: Mar 20 16:34:33 1995
From: "Michelsen, Teresa" - TEMI461 at ecy.wa.gov




While full albinoism is itself a recessive trait among humans and other
mammals, humans also have more limited birth "defects" that cause a lack of
pigmentation in human skin (patches of white skin are fairly common). Such
birth defects could be caused by a recessive trait or by exposure to
chemicals or other causative factors during reproduction or development.
Just generalizing to other animal species (a dangerous thing to do), a
random patch of white feathers could be caused by a similar birth defect.
There are examples of recessive genes that cause a lack of pigmentation in
certain parts of the body (e.g., eye color in _Drosophila_); however, these
recessive genes are well-known and repeatable. If it were genetic and
recessive, it would only appear in an individual bird if the genes of the
two parent birds both coded for white feathers in the same part of the bird.
I imagine this would mean that most birds that were partially white in a
given species would be partially white in consistently the same places. If
the pattern of white feathers appears to be more random, then the birth
defect theory might make more sense, since causative agents of birth defects
could act on an individual bird while it was developing in less predictable
ways. For example, the same types of birth defects that cause skin
pigmentation (or lack of it) in humans can appear anywhere on the body. An
added twist may be a genetic predisposition to a given type of defect among
certain species or races. For example, I have never seen a black person
with a white patch on their skin (something you might think would be fairly
obvious), though I have often seen caucasians with such. A genetic
predisposition to a type of birth defect that occurs during development
would explain a pattern of occurrence where some species of birds are more
likely to have white feathers, but have them in unpredictable locations.
This is probably separate (and in addition to) true albinoism, which is
almost certainly a recessive trait.

The above is patched together from a college education that was admittedly
some time ago. If I have made any incorrect statements about genetics or
developmental defects, please forgive/correct me!!

Teresa Michelsen
temi461 at ecy.wa.gov