Behavior

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Behavior

• Chapter 12

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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

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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

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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

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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?

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Animation Communication among neurons
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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

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Synapse
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Drugs Mimic Neurotransmitters
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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

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Normal Brain and One with HD
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Chromosomal Abnormalities

• Example fragile X syndrome mutation on X
  chromosome
• Causes autistic type behaviors as well as
  problems with aggression

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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

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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

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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

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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

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Concordance in Selected Traits
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Pedigree of Huntington Disease
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Animal Studies (1)

• Mice reproduce quickly, behaviors are observable
• May use recombinant DNA techniques
• Insert a human gene
• Mutate a mouse gene
• Change genes pattern of expression

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Animal Studies (2)

• Human gene for a protein associated with memory
  inserted into mice
• Transgenic mice improved maze running and other
  tests

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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

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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

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Pedigree of Family with Violent Behavior
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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

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Knockout Mice
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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

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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

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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

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Adult and Teenage Brains
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Spotlight on Law Mobley v. Georgia

• Stephen Mobley on trial
• Violent murder and armed robbery at Dominos
• 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