Behavioral Traits

Chapter Eight

Genetics of Behavior

Most behavioral traits:• Multifactorial

• More than one gene

• Genetic Heterogeneity– Different genes in different individuals

• Heavy environmental component

• Symptoms overlap between disorders

Genetics of Behavior

In other words, very complex!

Also:• Common

• Debilitating

Which is why we struggle to cure them

Behavioral Traits

Include:

• Mood (feelings)

• Personality

• Intelligence

• Communication

• Handling stress (coping)

• Mental Abilities

• Anxiety

Prevalence

Behavioral Disorders

• Arise from problems in central nervous system function

• Central Nervous System (CNS)– Brain – Spinal Cord

Neurotransmission

Synapse

Presynaptic Neuron Postsynaptic Neuron

5-HTTryptophan

Postsynaptic Receptors

Presynaptic Receptors

Vesicle of Neurotransmitter

Reuptake Transporter

Neurotransmitter

Intercellular Changes

Genetic Contribution?

How genetic is any trait?

• Examine sharing trait between relatives who also share genes

• MZ vs. DZ twins– Concordance rate

• Siblings/relatives of individual with trait vs. general population– Trait Prevalence

• Transgenic Animal Models

Mapping The Genes:

1. Linkage:- Marker and phenotype are correlated

2. Animal Models- Animal can be manipulated to show

phenotype

- Compare differences in genetics, matched to differences in phenotypes

3. Association Studies:- Are certain alleles correlated with phenotype?

Behavioral Genes

• Linkage narrows down region – Identifies QTL

• Candidate genes: – Within QTL– Involved in neurotransmission– Show differences between affected and

unaffected individuals– “make sense”

Specific Disorders

• Now we are going to go through some specific behavioral disorders

• Pay attention to:– Basics of the trait– What it is, how it affects a person– How we know trait is genetic– How genetic do we think trait is, if we know– What is evidence of gene involvement

Eating Disorders

• Anorexia Nervosa– Self perception/image is obese– Self starvation

• Bulimia– Binge and purge

• Muscle Dysmorphia– Self perception/image is too small/weak– Over-eat and/or over-exercise

Eating Disorders

• Twin concordance:– 40% MZ vs. 6% DZ

• Prevalence:– 6 to 10 % sibs vs. 0.5 to 2% population

• Heritability:– between .5 to .8

• Candidate genes:– Body image, self esteem (appetite?)

Sleep Disorders

• Narcolepsy– Fall asleep instantly, out of context

• Familial Advanced Sleep Phase Syndrome– Fall asleep at exactly same times each day

• Insomnia– Chronic inability to sleep

• Night Terrors– Extreme fear while asleep (not dreaming)

Narcolepsy

• Twin concordance:– 25% MZ vs. 0% DZ

• Heritability:– Around .33

• Animal Studies:– In dogs – identified a difference in receptor

• Candidate genes:– Hypocretin/orexin

FASPS

• Human Genetics:– Identified rare disorder in few large pedigrees– Linkage to Chromosome 2q

• Genetic Heterogeneity

• Heritability:– Around .33

• Candidate genes:– period gene (sets “biological” clock)

Insomnia

• Twin concordance:– 41% MZ vs. 16% DZ

• Heritability:– Around .4

• Obvious environmental effects– Overlaps with many other disorders

• Candidate genes:– Serotonin, period gene, anxiety/mood

candidates

Intelligence

• More subjective that practically any other trait

• Definitely has genetic component

• Strong environmental component

• Defined?– Logic/critical thinking– Math reasoning– Verbal fluency– Visio-spatial skills and memory

mental ability

Quantitative Trait

Intelligence

• Twin concordance:– 85-95% MZ vs. 40-50% DZ

• Chromosomal Abnormalities:– Cause mental retardation – genetic

• Heritability:– Adulthood = .8

• Candidate genes:– Genes within abnormal regions– Neurotransmission, N-CAM

Environmental Factors?

• Economic levels

• Culture background

• Parent’s education

• Parent’s success

• Nutrition/diet

• Geographical location/neighborhood

• Others?

The Bell Curve

• High heritability – strong genetic effect

• Ethnic differences in intelligence

• Therefore, genetic differences in races must cause differences in intelligence

• Minorities are genetically inferior

• What are problems with this argument?

Addictions

Physical and emotional need to continue a habit that is unhealthy:– Tolerance and Dependence

• Alcoholism

• Smoking

• Illicit drugs

• Gambling

• Sex, food, etc

Addictions

• Twin concordance:– 48% MZ vs. 2.2% DZ

• Heritability:– Between .4 to .6

• Brain Imaging Studies:– Brain responds to consumption and withdrawal– Limbic system

• Candidate genes:– Dopamine receptors, transporter, etc.

Mood Disorders

• Major Depressive Disorder– Feeling hopeless or sad– Based on no immediate environmental cause– Lack of appetite, sleep, attention

• Bipolar Affective Disorder– Alternating depressive mood– Manic mood – hyperactivity, restless, rush of

excitement

Mood Disorders

• Twin concordance:– 46% MZ vs. 20% DZ

• Prevalence:– 20 to 30% sibs vs. 5 to 10% population

• Heritability:– Between .4 to .6

• Candidate genes:– Serotonin, norepinephrine systems

Successful Drugs

Often with behavioral disorders treatment comes first, explanation comes second:

• Medications that “make sense”

• Medications that work on some symptoms

• Medications that gave a helpful side effect

Selective Serotonin Reuptake Inhibitors (SSRI)

Schizophrenia

• Loss of ability to control thoughts and perceptions

• Usually brought on by life stressor

• Delusions

• Hallucinations

• Disorganized behavior and speech

• Withdrawal from reality

Known Environmental Factors

Schizophrenia• Twin concordance:

– 46% MZ vs. 9% DZ

• Prevalence:– 9% sibs vs. 1% population

• Heritability:– Around .8

• Known chromosomal abnormalities

• Candidate genes:– Dopamine and Glutamate systems

Summary

• Behavioral disorders are multifactorial

• Often strong genetic contribution:– Twin concordance– Sib risk vs. general population risk– Chromosomal abnormalities/Animal models

• Strong environmental component too

• Difficult to map genes involved

• Candidate genes often guesses, based on knowledge of disease

Summary

Next Class:

• Homework – Chapter Eight Problems;– Review: 1,2,4,6– Applied: 1,2,5,6,7,9,11,14– Also – write out at least 2 questions

about material to review on Wednesday

• Review Chapters 1-8 and notes

Next Class:

Review Chapters 1-8

• Go through your review questions • Exam 1 – September 29th

• Pedigrees due October 13th