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Science Forum Index » Bio Evolution Forum » dominance hierarchy
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| g |
 Posted: Sun Feb 04, 2007 10:19 am |
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Guest
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This may be a question some of you know the answer to, already on this site.
If so, forgive my asking again, but
could there be examples of a gene that is dominant over a gene that is, in
turn, dominant over a THIRD gene?
If not, then that would suggest something about dominance... namely that it
might be a characteristic in and of itself.
If so, then that would suggest a different something about dominance...
namely that it might be simply a comparison of scale, or a mono-typic switch
which, if we could manipulate that switch we could change a recessive gene
into a dominant one, or vice versa, or both.
One who has not studied in detail how electrical storage batteries are
designed, and why they work as they do, might think of a positive pole as
"opposite" from a negative pole. HOWEVER, an understanding of the mechanism
of positivity and negativity informs us that a battery can be constructed
with three, four, or even more poles.
Unlike the simplistic some individuals have of political polarities (another
grossly misunderstood mechanism, a deeper understanding of which reveals
complex hierarchies of causality in any political determination) whether a
pole is positive or negative is purely relative to its place UPSTREAM or
DOWNSTREAM in direction of flow of electrons. (Further refinements on the
subject recomplicate it a bit, but for instant purposes, suffice it to say
that current flow during OUTPUT of a storage battery is predictable and in a
single direction.)
Anyhow, a battery with three poles, evenly spaced in relation to the
reactive plates in an acid solution, will put out TWICE the power from first
to last pole than from middle pole to upstream or downstream end pole. For
example, a batter can be constructed that provides 6 volts differential
between so-called negative pole to center pole, 6 volts from center pole to
far end pole, and 12 volts from one end pole to the other end pole.
If this old layman could think of that, then SURELY an expert microbiologist
has long since thought of it and has experimented to see if anything
analogous to that can occur with gene dominance.
If -- on the other hand -- nobody ever has wondered about this, and tried it
out... this old guy surely hopes some doctoral candidate might see some
potential in checking it out.
g |
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| Perplexed in Peoria |
| Posted: Mon Feb 05, 2007 6:55 am |
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"g" <gillawton@earthlink.net> wrote in message news:eq5f3k$o1d$1@darwin.ediacara.org...
Quote: This may be a question some of you know the answer to, already on this site.
If so, forgive my asking again, but
could there be examples of a gene that is dominant over a gene that is, in
turn, dominant over a THIRD gene?
Sure. Though I don't have a handy example.
Quote: If not, then that would suggest something about dominance... namely that it
might be a characteristic in and of itself.
It is not really a characteristic of a gene at all, it is a characteristic
of the relationship between an allele and a phenotypic trait, with reference
to alternative alleles at the same locus.
I will assume you understand the genetic basis of A-B-O blood types in
humans. For illustration purposes, let us consider some hypothetical
relationships between blood type and disease resistance. Assume that
blood type A confers resistance to rubella, blood type B confers resistance
to smallpox, blood type AB confers resistance to both, and blood type
O protects against neither but confers some resistance to plague.
In this case, the gene for A is dominant over the gene for B or O with
respect to the trait of rubella resistance. But B is dominant over A
and O with respect to the trait of smallpox resistance. |
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| Alan Meyer |
| Posted: Mon Feb 05, 2007 6:55 am |
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g,
I'm not sure you're on the right track here. Here's my
inexpert understanding of what's going on.
Consider two alleles (small variations) of a gene in a plant,
one on a chromosome inherited from the pollen grain and
one from the ovary of the mother plant.
One of the alleles is expressed as a protein that turns the
plant's flower red. The other allele does not produce this
protein.
So here's what happens: If one or both alleles are of the
red producing kind, the plant produces red flowers. However
if _both_ are of the other kind, the plant does not produce
red flowers - the flowers have some other color, whatever
it would be in the absence of the red pigment.
The red producing version of the gene is "dominant". It's
not that "dominance" is some special property of that
allele, it's just that it so happens that if that allele is present
enough red pigment will be produced to color the flowers
red. That is so even if there is only one of the two alleles
with that configuration.
As to whether a third value could play a role, the answer is
clearly yes - in several different ways. Although every
organism only has two alleles for a gene (polyploidy excepted)
it is often the case that more than one gene is involved in
determining an outcome.
As I understand it, there are three genes involved in skin
color, producing a total of exactly seven human skin colors
(plus albino). We perceive more than seven shades because
people have different amounts of suntan, aging, or other
causes of skin color change.
In other cases, only two alleles are involved, but they produce
three outcome values. For example, there are some plants
that produce red, pink, or white flowers. One red allele is
enough to generate some red pigment, but not enough to
turn the flower red. Both alleles must be actively expressed
to get enough pigment for a red flower.
So "dominance" is not really a property of alleles, it's just
a reflection of the fact that, for many genes, if one particular allele
is present that has a particular effect, it doesn't matter whether
the other allele has that effect or not. The "phenotype" will be
apparent.
Have I got that right? Does it help?
Alan |
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| g |
| Posted: Tue Feb 06, 2007 8:51 am |
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"Perplexed in Peoria" <jimmenegay@sbcglobal.net> wrote in message
news:eq7nh9$1k3v$1@darwin.ediacara.org...
Quote:
"g" <gillawton@earthlink.net> wrote in message
news:eq5f3k$o1d$1@darwin.ediacara.org...
This may be a question some of you know the answer to, already on this
site.
If so, forgive my asking again, but
could there be examples of a gene that is dominant over a gene that is,
in
turn, dominant over a THIRD gene?
Sure. Though I don't have a handy example.
If not, then that would suggest something about dominance... namely that
it
might be a characteristic in and of itself.
It is not really a characteristic of a gene at all, it is a characteristic
of the relationship between an allele and a phenotypic trait, with
reference
to alternative alleles at the same locus.
I will assume you understand the genetic basis of A-B-O blood types in
humans. For illustration purposes, let us consider some hypothetical
relationships between blood type and disease resistance. Assume that
blood type A confers resistance to rubella, blood type B confers
resistance
to smallpox, blood type AB confers resistance to both, and blood type
O protects against neither but confers some resistance to plague.
In this case, the gene for A is dominant over the gene for B or O with
respect to the trait of rubella resistance. But B is dominant over A
and O with respect to the trait of smallpox resistance.
THANK YOU, Perplexed!
I have read up on, and forgotten details of, details of blood types and
the medical aspects... more than once.
Right this very minute, I'm forcing myself to go back and reread a course
on general biology. Then I shall force myself to stick with the whole
course on genetics (entry level, which won't get me where you are with
it). I've GOT to read Dawkins and take time to digest... so will put that
next... Then, I am not sure what I shall force myself to stick with next.
But can I stick to a regimen?
So far, I have speed-read into these things at maybe a page a minute, and
it just ain't wurkin'.
AS ALWAYS your help is both enormously helpful and poignant.
g |
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| g |
| Posted: Tue Feb 06, 2007 8:51 am |
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Guest
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"Alan Meyer" <ameyer2@yahoo.com> wrote in message
news:eq7nha$1k8m$1@darwin.ediacara.org...
Quote: g,
I'm not sure you're on the right track here. Here's my
inexpert understanding of what's going on.
Consider two alleles (small variations) of a gene in a plant,
one on a chromosome inherited from the pollen grain and
one from the ovary of the mother plant.
One of the alleles is expressed as a protein that turns the
plant's flower red. The other allele does not produce this
protein.
So here's what happens: If one or both alleles are of the
red producing kind, the plant produces red flowers. However
if _both_ are of the other kind, the plant does not produce
red flowers - the flowers have some other color, whatever
it would be in the absence of the red pigment.
The red producing version of the gene is "dominant". It's
not that "dominance" is some special property of that
allele, it's just that it so happens that if that allele is present
enough red pigment will be produced to color the flowers
red. That is so even if there is only one of the two alleles
with that configuration.
THANK YOU. I do recall, from somewhere in my impulsive and moderately
randomized speed readings that Mendel was quite lucky to have dealt with a
simple red versus white kind of whatever I mean when I say the word
"dominance."
As best I recall (and I shall go back and dig more thoroughly soon) there
are some situations in which one gets a hybrid that has a characteristic
that is intermediate. Had Mendel chanced to work with one of those, he
might have
gotten the result he anticipated, rather than a clearly binomially chartable
set of ratios.
Also, as best I recall, some characters (characteristics) of plants and
animals are very complex as to genetic
etiology. Had Mendel chanced to pick one of these, his poor head might have
ended up as befuddled as mine...
Thanks for jogging these speed-read fragments.
So many questions, so many books... so little capacity to learn it all... so
little time (:>).
You are kind to offer help.
g |
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| Guest |
| Posted: Wed Feb 07, 2007 8:25 pm |
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Quote: In this case, the gene for A is dominant over the gene for B or O with
respect to the trait of rubella resistance. But B is dominant over A
and O with respect to the trait of smallpox resistance.
Do B and O genes express the same amount of rubella resistance?
Do A and O genes express the same amount of smallpox resistance? |
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| Perplexed in Peoria |
| Posted: Thu Feb 08, 2007 8:42 am |
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<drosen0000@wahoo.com> wrote in message news:eqefnt$1ji0$1@darwin.ediacara.org...
Quote: In this case, the gene for A is dominant over the gene for B or O with
respect to the trait of rubella resistance. But B is dominant over A
and O with respect to the trait of smallpox resistance.
Do B and O genes express the same amount of rubella resistance?
Do A and O genes express the same amount of smallpox resistance?
In my hypothetical example, 'yes' to both questions. B and O express
the same amount (zero) of rubella resistance. A confers resistance
whether present in single or double dose. |
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