Guy F. Barbato
gfb1 at psu.edu
Mon Dec 5 10:09:55 EST 1994
Dec 4, 1994 <toby at u.washington.edu> responded to an email reply of mine
<gfb1 at psu.edu> via email....i didn't mean to take the discussion off the
newsgroup, its just my genotype-limited IQ can't seem to tell the difference
between "follow" and "reply" ... : ) .... sorry ---- guy
> perhaps you didn't specifically mention narrow or broad sense at all. Using
Read the posts. I specifically said that broad-sense H^2 was what
> vaque terminology in posts, then pleading innocence for not being more
> specific later smacks of the "oversimplification", if not "special pleading"
> : )
Please read what I wrote.
> however, additive variance is *not* irrelevant to broad sense heritability, it
> is a portion of the total genetic variance.
Additive variance can be zero to 1 without affecting the *ability* to
calaculate broad sense heritability. If you want to partition the
*genetic* variance, fine. It's not necessary to do so to calculate
the relative contributions of genetics and environment to a phenotype.
> >>each child enters school with
> >>certain attitudes and abilities determined by his family and environment,
> >>and to some undetermined (and undeterminable) degree due to genetics.
> > ^^^^^^^^^^^^^^
> >Why is this so?
> except for special circumstances (e.g., single gene traits or chromosomal
> abnormalities) one cannot characterize the genetic contribution to an
> *individual* phenotype
You might want to bone up on QTL mapping. Lander and Botstein (1989) Jan
Genetics is a good place to start. See my upcoming paper in the Feb
Genetics for an extension of this work to trees. There's no conceptual
reason why a single gene trait represents a "special circumstance",
as has been shown numerous times.
> this is the difference between an optimist and pessimist.
An idealist and a realist. In theory, theory and experiment are
identical. In practice, they're not.
> IMHO this is what the public school system was originally designed to
> accomplish. not fantasy, but a lifetime goal
Entropy is winning this fight.
> >Are you claiming that the twin models overestimate heritability due to
> >non-additivity, or that only the *proportion* of nonadditive genetic
> >variance is biased upward relative to the total genetic variance? Unless
> >you're interested in breeding, the partitioning of *genetic* variance
> >components isn't necessary to determine the degree of genetic control
> >of a trait.
> hmmm....yes, no, yes (but not people), not.
> heritability determined from twin studies overestimates heritability due to
> non-additivity (see Falconer or Ehrmann)....this has been known by dairy
> breeders since the late '40s early '50s.
You're talking about narrow-sense heritability. Don't think like a
breeder who can't clone -- think like a geneticist!
> further, the relative proportion of the types of genetic variation that are
> exhibited by a trait provide information for interpretation of the
> evolutionary history of the trait (see lewontin's work). perhaps more
> importantly, the type of genetic variation defines the experimental
> methodology necessary to elucidate the nature of the genetic variation (both
> in a quantitative sense re:mather and jinks and in a biochemical sense
> re:lander and botstein) the wrong experimental design combined with and
> incorrect model applied to the wrong trait = disaster.
Lander and Botstein say nothing about Q trait inheritance in a biochemical
sense -- the resolution of the technique doesn't permit it.
> >>ANYWAY, the genetics of individual differences (in humans) is an interesting
> >>academic problem which is probable insolube without the randomization of
> >>environments....or maybe a selection experiment <ok...it was a bad joke>
> >You might want to check into the trisomy 21 literature, which seems
> >to explain individual differences in human intelligence
> >in a very limited sense, and for which negative selection is performed
> i agree, very limited. and not relevant to the population at large.
Why not? That's like saying a translocation that causes a defect
in a tumor suppressor is "not relevant". The key is that intelligence
has a genetic component. See Helentjaris' recent work in maize
height QTLs vs. classical dwarfing loci.
> I don't know your background or training (obviously, or, perhaps, not-so-
> obviously) i am a quantitative geneticist ... i used to say behavioural
> geneticist, but they can't get real jobs. : ) ...
> it is always curious to me the manner in which one field of study uses/adopts
> methodologies from other fields, many times it is the technical definition of
> common terminology that has intrinsically different meanings (and basic
> assumptions) in each field. at least in this case (i.e., genes and
> intelligence) i defer to the commentary by Jerry Hirsch on potential
> pitfalls and pratfalls in this line of inquiry...see: To unfrock the
> charlatans in SAGE: race relation abstracts 1981...jerry was a bit criticized
> by the traditional animal behavior geneticists for getting into this argument,
> but his point of view reflects mine as well.
If you want to discuss this further, how about posting to the net.
I'm a molecular geneticist and tree breeder, but I know enough QG
to undrstand that 1) things are not always as simple as they appear
and 2) things are not always as complex as they appear. See my Feb
95 Genetics paper.
toby at u.washington.edu
G. F. Barbato Phone: (814)-865-4481
Dept. Poultry Science FAX: (814)-865-5691
Penn State Lab: (814)865-5691
University Park, PA Email: gfb1 at psu.edu
//// On induction, or 'Why do you believe the sun will rise tomorrow?"
< * ) The farmer who has fed the chicken every day throughout
\ \___/// its life at last wrings its neck instead, showing that the
( --- ) more refined views as to the uniformity of nature would
\/ \/ have been useful to the chicken. ----- Bertrand Russell
More information about the Bioforum