PSYC 3102: Introduction to Behavioral Genetics
Lecture 3
Conclusions of the Course
Will see time and time again through course, CRUCIAL points of class!
These are based on data, and are not philosophical
1. Every human behavior studied thus far has an important environmental
input/component
 substantive behaviors - personality traits, cognitive ability, psychopathology,
attitudes
 implications: there is no psychopathology that is genetic; schizophrenia, bipolar
disorder, alcoholism, etc. are not genetic; personality traits are not genetic; IQ is not
genetic
 data: identical twins do not behave identically; correlation for twins is less than 1.0;
Rmz<1.0 (eg. If one twin is schizophrenic, there is about a 50% likelihood that the
other twin is; correlations for most personality traits in identical twins are about 0.50.6)
2. Almost every substantive human behavior has an important genetic
input/component
 This includes all the behaviors mentioned above and:
o Probability of divorce
o Combat exposure in Vietnam
o Amount of TV watched
o Religious attitudes, etc.
 Data for this? Identical twins concur more than fraternal twins (More Below)
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Nature vs. Nurture
NOT Justified
Nature versus Nurture debates are STUPID and non-scientific
BOTH combine to produce phenotypes
All behavior involves a dynamic interplay between nature and nurture
Analogy: Is lemonade: a) water or b) sugar or c) lemon juice?
o It’s a SOLUTION of ALL components
Behavior is also a solution, a dynamic interplay, an orchestra
Environment interacts with gene expression, can ‘turn on and off’
o Ex: Cortisol levels increase with anxiety and fear, watching a scary movie
(environment) can cause cortisol levels to increase, cortisol then interacts
with cells to turn certain genes (expression) on and certain genes off
Therefore the current research consists of HOW genes and environment
combine/interact
HOW do genes INFLUENCE behavior
Getting at the “HOW”
Wet Labs:
 Molecular genetics
 Neuroscience
 Look for individual genes—how do they influence behavior
 Big in psychopathology
Genetic epidemiology
 Mostly statistical
 “Dry” labs
 Twin data analysis
o Example -- Combat Exposure in Vietnam:
-Identical twins are more concordant that fraternal twins for having been in
combat in Vietnam
-- There isn’t a ‘combat exposure in Vietnam’ gene, rather, look at factors
likely to increase or decrease the likelihood of combat:
Education/cognitive ability (being in school prevents drafting; having
education may place some away from front lines, such as MDs)
Health/physical/psychological problems (screening test for military)
Personality traits (risk taking, aggression, obedience)
-- All these factors have genes influences
-- Genes don’t influence combat expose directly, but influence other factors
-- No one factor determines combat exposure, but add them up, weight the
factors and you will increase or decrease the probability
Genes
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Proximal Variables
Distal Variables
Cognitive Abilities
Physical Traits
Personality Traits
Combat Exposure
Another example (more substantive):
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Genetics of Anti Social Behavior
 Associated with criminal behavior
 But, more those that don’t ‘play by the rules’
o
BMW scenario
 Red, top down, keys in ignition, no one in sight
 + group of teenagers
 What would you do?
 Pro-social behavior—take keys out, write down plate #, give keys
and info to cops
 Anti-social behavior—steal, take for joyride, take to chop shop and
sell off parts
 Genetic influences on behavior—not an innate sense of do this or that
to an unattended BMW, but rather aspects of impulsivity,
fearfulness, anxiety, risk-taking
 Not only an individual’s influence of own genes, but those of the
group—peer pressure, their genes influence your behavior
The big question is HOW? How do genes influence behavior
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Minnesota Twin Study example:
o MZ twins raised apart in England (one in North, other in South)
o Met for first time in Minnesota to be part of the twin study
o Arrived within an hour of each other at the airport… wearing the exact
same dress
o But, take into consideration—they look the same, may pick the same dress
due to the color, cut, etc. appealing to the physical attributes they share, as
well as personality traits (flamboyant/extroverted vs.
conservative/introverted)
Biology of the Gene / Molecular Genetics
The Cell
Important Structures
Cell wall/plasma membrane
 Molecules surround and envelope the cell
 dynamic structure, not just a plastic baggie
 Have molecules with function: studded with channels and receptors with the role of
sentinels (communication going in or out) or gatekeepers (let selected molecules in
or out of cell)
Cytoplasm
Nucleus
 “castle keep”
 Storage place for DNA
 DNA doesn’t come out (except when cells divide)
Endoplasmic Reticulum
 Densely packed with ribosomes
Ribosomes
 Protein “factories”
 Where proteins get synthesized
Mitochondria
 Contain their own DNA (mtDNA)
 ~16,000 nucleotides
 Gives use more efficient metabolism, lets us use oxygen for chemical reactions
 Maternally transmitted (comes in egg)
o Tiny exceptions, if sperm does transmit, it won’t be much
o Used in anthropological studies, migration patterns inferred
The Neuron
Actually comes in all shapes and sizes, this is just a schematic, cells can be very different
Has plasma membrane, nucleus, etc.
Also has axon, dendrites
Vesicles
 Storage ‘container’
 Holds chemicals called neurotransmitters
Communication occurs through neurotransmitters
Neurotransmission
Neurotransmission
Synapse
 Space between neurons
Pre synaptic Neuron
 Depolarization, then fires
Neurotransmitter
 Binds with specific receptors (lock and key)
 Will incur chemical changes
 There has to be a mechanism to stop/get rid of neurotransmitter
o Enzymatic breakdown—changes it to a waste product
o Reuptake—neurotransmitter binds with transporter and is returned to the
pre synaptic cell (usually re-stored in vesicle)
Post synaptic Neuron
 Binding influences opening of ion channels
 Biases electrical potential of the neuron, stimulates or inhibits firing
 Binding also induces 2nd messenger system
o Cascade of chemical changes
o Influences extent of genes being turned on or off