Behavioral genetics
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Transcript Behavioral genetics
Behavior
Chapter 12
Central Points
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
Twin studies are an important part of behavioral
genetics
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
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
Multiple backgrounds:
psychologists
psychiatrists
neuroscientists
statisticians
molecular geneticists
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 Schizophrenia
Pedigree of Alcoholism
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
Pedigree of Homosexuality
Genetic Causes of Sexual Orientation
Used twin studies, chromosomal analysis, and
pedigree analysis
Suggest genetic component to homosexual
behavior
Used linkage and pedigree studies to ID area on X
chromosome associated with homosexuality
Foundation for further work on genetics and
homosexuality
Concordance of Homosexuality
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
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
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
Video: ABC News: Heart healthy
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
Case B: Important Conference on Hold
“Genetic Factors in Crime: Findings, Uses, and
Implications”
Protests caused meeting to be cancelled
What should the scientists do?
What are the important issues?
See the textbook for further questions on this
case
1966: Richard Speck
Tried and convicted of killing eight student
nurses
Attorney prepared defense trying to use XYY
karyotype as argument against death penalty
Speck did not have the XYY karyotype
Many unanswered questions about genetics and
behavior remain
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
Areas that control
impulsive behavior
(a)
(b)
Fig. 12-1, p. 199
Ethical and Legal Issues
Ethical and Legal Issues (cont.)
Spotlight on Law: Mobley v. Georgia
Stephen Mobley on trial
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•
•
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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
Mobley’s and MAOA Deficiency Pedigrees
Spotlight on Law: Questions
Women in Mobley’s family are identified with
trait. Could this be MAOA deficiency?
Would you have allowed the testing?
How does this relate to a genetic cause of
crime?
See the textbook for further questions on this
case