Central Points (2)
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Transcript Central Points (2)
Behavior
Chapter 12
Central Points (1)
Behavior is a reaction to environment
Animals and humans have similar behaviors
Brain chemicals important in human behavior
Single gene or groups of genes can affect
behavior
Central Points (2)
Twin studies are an important part of behavioral
genetics
Courts are unclear on how to address the issue
of genetics and behavior
Case A: Twins Found Strangely Alike
University of Minnesota Twin Study Group,
studying twins reared apart
“Two Jims”: amazing number of physical and
other similarities
Twin studies assist in the study of the genetics
of behavior
12.1 Behavior
A reaction to stimuli
Human behavior similarities to animal behavior,
response more variable, difficult to study
Behavioral genetics: study of the influence of
genes on behavior
Which more important: genetics or environment?
Animation: Communication among
neurons
12.2 Neurotransmitters
Brain chemicals that can change our moods and
actions
Neurotransmission: Neurotransmitters released
when certain neurons in the brain fire
Impulse travels to synapse, neurotransmitter is
released
Increases or decreases in the release of the
neurotransmitter, may change behavior
Synapse
Drugs Mimic Neurotransmitters
12.3 Changes in Genes Changes Behavior
Chromosomal abnormalities, single-gene defects,
and multigenic conditions can alter behavior
Example of single-gene defect: Huntington disease
(HD)
Codes for protein huntingtin, necessary for the
survival of certain brain cells
Symptoms of HD: involuntary movements and
progressive personality changes
Normal Brain and One with HD
Chromosomal Abnormalities
Example: fragile X
syndrome mutation
on X chromosome
Causes autistic type
behaviors as well as
problems with
aggression
Schizophrenia: A Multifactorial Condition
Collection of mental disorders
Many symptoms including hallucinations,
delusions, disordered thinking, changed behavior
Genes associated with schizophrenia found on X
chromosome and other autosomes
Also possible environmental component
12.4 Studying the Genetics of Behavior
Search to find the genetic influences, also
studied by psychologists and psychiatrists
Medical geneticists study genetic basis for
medical illnesses
Differences between medical and behavioral
geneticists blurring
Now treat depression as a physical illness
Identical Twins (Monozygotic)
Identical twins have identical genomes
If a specific trait or behavior is same in both
twins, most likely significant genetic component
If twins raised in separate environments and
have different behavioral traits, traits have a
significant environmental component
Concordance in Monozygotic Twins
If one identical twin is alcoholic, 55% chance other
twin will be alcoholic regardless of environment
Concordance: how often a trait occurs in both
members of a pair of twins
Genetic trait, cystic fibrosis concordance = 1.0
Concordance helps establish whether or not trait
has genetic basis
Concordance in Selected Traits
Pedigree of Huntington Disease
Animal Studies (1)
Mice reproduce quickly, behaviors are observable
May use recombinant DNA techniques
Insert a human gene
Mutate a mouse gene
Change gene’s pattern of expression
Animal Studies (2)
Human gene for a protein associated with
memory inserted into mice
Transgenic mice improved maze running and
other tests
Case A Questions
Why were these two men a perfect set of twins
to study behavior?
Do you think the evidence shows the behaviors
listed in the case are 100% genetic?
Can you see any problems studying twins raised
apart?
See the textbook for further questions on this
case
12.5 Single-Gene Defect and Aggressive
Behavior
Large family with aggressive and violent behavior
Only in men, many committed violent offenses
Mapped to short arm of X chromosome
Gene encodes monoamine oxidase type A
(MAOA) that breaks down neurotransmitters
Mutated form of gene, MAOA deficiency
Pedigree of Family with Violent Behavior
Knock out Mice for Serotonin Receptors
Failure to rapidly break down neurotransmitters
such as serotonin
Does not allow the normal transmission, disrupts
normal functions in the nervous system
Can cause abnormal behavior
Researchers deactivate (“knock out”) serotonin
receptor gene in mouse
• Knockout mouse aggressive to unfamiliar mouse
Knockout Mice
12.6 Legal and Ethical Issues
Not sure what causes aspects of behavior
Courts finding it difficult to deal with topic
Experts do not agree on findings, individual
courts cannot decide how it will be used
If certain genes or groups of genes cause
someone to commit a crime, motive no longer
relevant
XYY Syndrome
Prisoners incarcerated for violent crimes showed
higher percentage of men with XYY syndrome
Studies done on relationship between criminality
and XYY individuals
Generally taller and perhaps more aggressive,
but this does not mean they are criminals
Information incomplete
Other Questions
If criminal or antisocial behavior is genetically
controlled, how can someone be rehabilitated?
Roper v. Simmons: an amicus curiae brief
presented
• Area of brain controlling impulsive behavior
underdeveloped in teens
• Therefore unable to realize actions
Most judges and juries considered genetic
predisposition to crime junk science
Adult and Teenage Brains
Spotlight on Law: Mobley v. Georgia
Stephen Mobley on trial
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Violent murder and armed robbery at Domino’s
History of rape, robbery, assault, and burglary
Aggressive behavior prevalent in his family
Wanted to be tested for mutation of MAOA gene
Court denied, genetic connection not at level of
scientific acceptance to justify its admission