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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 Tryptophan Postsynaptic Neuron 5-HT Intercellular Changes Neurotransmitter Postsynaptic Receptors Presynaptic Receptors Vesicle of Neurotransmitter Reuptake Transporter 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? mental ability – Logic/critical thinking – Math reasoning – Verbal fluency – Visio-spatial skills and memory 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