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 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