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-HT Tryptophan 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 % 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 29 th Pedigrees due October 13 th