Behavioral Genetics
• Temperament – that portion of a person’s
personality that has an organic, and
therefore genetic, basis. It is has been
acknowledged for centuries that some
portion of the personality has an organic
basis, e.g. personality differences between
men and women. It is obvious that some
of these differences can be attributed to
specific proteins, e.g. the hormones
testosterone and estrogen.
Chronic and Bipolar Depression
• Genealogy of a family from the Central Valley of Costa
Rica. Deceased persons are marked with a slash.
• It has been difficult to identify the specific
genes behind bipolar depression because
it is a polygenic trait, a trait caused by the
joint action of multiple genes.
The midbrain (mesencephalon): center for
emotions and sex
Synapses, neurotransmitters, and
receptors
Novelty- or Thrill-Seeking, and Addiction
Dopamine synthesis
• People who psychologists would describe
as thrill, or novelty seekers have been
shown to have a mutation of the D4DR
receptor allele, found on chromosome 11.
• All addictions involve affecting the release,
reuptake, or regulation of dopamine.
• Reuptake: the transporting of a
neurotransmitter back inside a dendrite by
means of transporter protein.
Dopamine and addiction
Serotonin and Depression
• Serotonin – Synthesized from the amino
acid tryptophan.
• Is involved in both relaxation and
aggression.
• Selective Serotonin Reuptake Inhibitors:
Zoloft, Prozac.
• There is controversy about the role played
by the serotonin transporter in chronic
depression – whether it is too efficient at
transporting serotonin (the majority
opinion) or defective in transporting
serotonin (Dean Hamer), in which case
Prozac and Zoloft should be seen a
synthetic serotonin transporter proteins.
IQ and Identical Twins
• Beginning in the 1970’s, Thomas
Bouchard and colleagues at the University
of Minnesota began gathering data on
monozygotic (identical) twins put up for
adoption and raised in separate
households (MZA’s).
• Any similarities shown by the twins would
be due to shared genetics, any differences
would be due to the environment.
General Outcomes
Twin studies have established the overriding
influence of genes on
• Schizophrenia.
• Male homosexuality (not lesbianism).
Outcomes for IQ
• Nobody denies that there is a genetic
component to IQ.
• Nobody denies that there is a significant
heritability factor to IQ.
• Everybody agrees that intelligence is
polygenic – probably involving hundreds of
genes.
IQ and sex differences
IQ and the Achievement Gap
• The race concept does not have biological
validity.
• In measures of academic achievement in
the US there are consistent and persistent
differences between average scores of
broad ethnic populations.
• Though it is accepted that it plays some
role, socioeconomic status is not held to
be the chief cause of this order.
• Debate continues to rage about the
relative contribution of genes and the
environment to this achievement
hierarchy.