Re: (newbie) Basic question




"Anon." bob.ohara@xxxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:-

Guy Hoelzer <hoelzer@xxxxxxx>
... If a trait is under the influence of many genes it can
be genetically controlled without having almost any heritability.

JE:-
Please provide an empirical example.

GH:_
Number of limbs in humans.

JM:-
Which raises the question of just what it means for a trait to be
"genetically controlled." (To say nothing about what it means for
a trait to be "heritable".)

BOH
That's easy: create a counterfactual. Knock out a gene, and see if it
changes the trait. OK, there are problems if the effect is to kill =
the
organism, but I think these cases should be (mostly) obvious.

JE:-
Bob's answer was misleading. Removing a gene that has a non additive
association to a set of genes only provides a very rough indication as =
to
what that gene actually does and how it may have evolved. Regarding the
genome as just a gene knockout "black box" does not get you very far. In
fact this approach has given many "good" genes a "bad" name. Many people
actually think that genes only code for genetic disease. Real synthetic
genetics requires a much more imaginative approach. Like reconstructive
archeology a valid synthetics approach cannot remain content to view the
phenotypic rubble produced by a knockout mutation and just leave it at =
that.
TESTABLE hypothesis have to be generated as to how and why.=20
=20
The argument might be made that during the period when thalidomide
was being prescribed in Europe, the limb count in humans was
environmentally controlled. Or, after visiting a VA hospital, you
might make that argument today.

Multiple causality is possible too!
I wonder if you're confusing genetic control of traits with genetic
variation in traits. I think almost all traits can be influenced by
both genetics and the environment, so in that sense they are always
controlled by both.

JE:-
I don't think that anybody disagrees that both are always involved. =
However
just saying that does not help very much unless you can provide a =
hypothesis
as to how they may work together. My hypothesis provides a simple start:
genes limit while the environment controls. Genes only provide heritable
limits for traits. The environment develops each trait within this set =
of
limits as Waddington described. Non plastic traits are much easier to
measure for their heritability than plastic traits but only because =
their
upper and lower limits remain close together. As Darwin noted, nothing =
in
living nature is ever exactly the same. IOW each trait is plastic to a
greater or lesser degree. The fact that wider limits befuddle synthetic
genetics is not an issue of substance unless this discipline simply =
deletes
them within uncorrected oversimplified models (which it does). =20

Regards,

John Edser
Independent Researcher

edser@xxxxxxxxxxxxxx

On Tour: Hong Kong -- Amsterdam -- Edinburgh


.

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