Heritability

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14 Δεκ 2012 (πριν από 4 χρόνια και 9 μήνες)

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HERITABILITY

Is it all in the GENES?

What is heritability?


Review…


An estimate of the proportion of the total variance in
some trait that is attributable to genetic differences
among individuals within a group.


In other words…when looking at a group, how much of a
certain trait is genetic vs. environmental?


Key points:


1. Only applies to a group living in the same
environment


2. DOES NOT apply to individuals, only to variations
within a group


3. Even highly heritable traits can be modified by the
environment

How do we test heritability?


Twin Studies


Why?


Why identical vs. fraternal? What would each
show us?



Adoption Studies?


Why?

Is your I.Q. genetic?


Intelligence Quotient


For many years calculated as:


Mental age/chron. Age X 100.



Is this a good way?


What about other ways of showing intelligence?


Biases?



Twin studies results:


Identical twins scores correlated more than fraternal


Adoption Studies:


Children correlated more with biological parents than
adopted parents.


I.Q. tests as a way to further
RACISM


HH Goddard’s tests on immigrants


The Bell Curve


Remember Phrenology?


Eugenics


applied
science
or the
bio
-
social movement
which
advocates the use of practices aimed at improving the
genetic composition of a population



Reading from
“Race” is a Four
-
Letter Word: the
Genesis of the Concept

Flaws in Heritability
Estimates


Most groups compared to mainly white
samples.



People as Tomato Plant metaphor:


(
pg

107!)

Genes and Personality


Heredity and Temperament


Temperament = how we typically respond to our
environment



Jerome
Kagan

did research on infant temperaments
and how that would affect people later in life


20% all babies highly reactive (excitable/nervous)


20% all babies highly
NONreactive

(laidback/curious)


Other 60% are somewhere in between



Reactive children…mild stressors caused more action in the
sympathetic nervous system, more norepinephrine
(adrenaline) and cortisol (increases blood sugar)

Heredity and Personality
Traits


Trait



habitual way of thinking, behaving, and feeling



Raymond B.
Cattell’s

Factor Analysis studies
supported the idea of the
BIG 5


1. Introversion vs. Extroversion


2. Neuroticism/ negative emotionality


3. Agreeableness


4. Conscientiousness


5. Openness to experience

Final Thoughts


If many studies show a .5 correlation between
a trait and genetic inheritance, that means
the other .5 of our make
-
up is influenced by
our environment.



Some studies my underestimate the impact
of the environment


Even traits that are highly heritable are not
rigidly fixed and can be modified by
experience.


“The wave of acceptance of genetic influence
on behavior is growing into a tidal wave that
threatens to engulf the second message of
this research: These same data provide the
best available evidence for the importance of
environmental influences” (
Plomin
, 1989).

Discussion Questions:


***Get into your Group Trip to the Australian
Outback***



1
. Just because a behavior is universal doesn’t
mean that there is necessarily a genetic basis for
the behavior. Geneticist Richard
Lewontin

point
out that if 99% of
Finnish
are Lutheran, it doesn’t
mean that Finns have a gene for Lutheranism.
What other behaviors are universal (or almost
universal),
but are unlikely to be genetically
determined?


2. Suppose that scientists developed a
genetic test that would tell prospective
parents whether they were carriers of a gene
that contributes to obesity. Should this test
be routinely offered to couples? What about a
test that could predict lower than average
intelligence? More generally, what are the
consequences to individuals and to society of
genetic engineering?



3. Evolutionary theory argues that variability
is important for the ultimate survival of a
species. But some would use genetic
engineering to reduce variability and
eliminate undesirable characteristics. What
might be the possible problems with this
approach? Can you imagine a scenario in
which a genetic “flaw” resulting in obesity, for
example, might be adaptive?



4.
If a gene is found for a predisposition to
antisocial behavior, should this finding
change the way we deal with criminals? If so,
how?