Behavior Chapter 12 Central Points 1 Behavior is
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
- Slides: 30