Download Behavioral Traits

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?
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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
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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