Hi again,
I would like to add to my previous posting that the point about
mutations producing new colors versus mutations preventing the
production of a pigment is rather a semantic one, though in some
circumstances an important one.
Cheers
Andrew
Andrew Hobbs wrote:
Hi,
I would disagree with Phillip's sentence 'There is also the aspect
that "mutations have produced a wide range of new colours" is at least
in most cases wrong as well '
If a bird is green because it produces a blue and yellow pigment, and
a mutation gives rise to a blue bird, then the mutation has given rise
to a new color; The mutation may have caused the loss of yellow
pigment as he clearly points out in the rest of the paragraph, but it
has definitely given rise to a new color, one that didn't exist before
(at least in this bird).
Secondly I am intrigued by the sentence " ......... before such wide
publicity of the appalling non-scientific methodology used in the
whole peppered moth saga was exposed, .................." about the
paragraph which is quoted as
"Only very rarely does a mutational change assist an organism to
survive. In the case of the Biston betularia moth, for example. it is
""thought"" that the black variety originally arose as a result of a
mutation. This mutation proved to be beneficial for the moth, as its
environment was changing at the same time.........."
What exactly is this "appalling non-scientific methodology" with
regard to the peppered moth.
Andrew Hobbs
Michael Tarburton wrote:
g'day All
Phillip veerman & I have engaged in a little dialogue about the text
(& what they might have meant) that made this claim. Some
clarifications have been made that might be of some use to some of
you so I forward them to the list.
Cheers
Mike Tarburton
Hi Mike,
Thanks for that. It appears that I was on the right track partly
because I was wondering WHY a book would make such a statement, as in
why would a text book bother to mention what colour budgerigars are.
Even if the point is worth making, it is very poor quality research,
understanding and/or editing. There is also the aspect that
"mutations have produced a wide range of new colours" is at least in
most cases wrong as well In terms of the word "produced". Most (or
all?) the colour variants that are now established in captive
populations are not the result of producing new colours as much as
loss of the ability to make the standard colours. So blue birds are
blue not because of a new gene producing blue but due to the loss of
the ability to make yellow pigment, so that the parts that normally
show as green now show as blue, the genes to produce the blue
structural colour were always there. Likewise yellow birds are yellow
not because of a new gene producing yellow but due to the loss of the
ability to make blue structural colour, so that the parts that
normally show as green now show as yellow, the genes to produce the
yellow were always there. These are the most basic features, there
are many other variants further enhancing those two.
This principle comes in potentially useful in regard to a wild bird
of any species that has colouration different from the normal. Of
course hybridisation is another quite different source of oddities.
Maybe this extra comment could go to the B-A list to fill in the
story. That is up to you, as in you first put it on.
Philip
|
