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