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Chapter 8-1
Symptoms- begins as a flu-like illness lasts at least 6 months causes disabling fatigue- bedbound, unable to carry on
with routines. Reports of severe physical illness or emotional trauma
prior to fatigue. Genetics research study has shown this is real. CFS patients-
make too little cortisol (stress hormone) make too much serotonin (induces sleep and calms)
2006- Research found 3 genes – one codes for receptor to bind stress hormones, two affect serotonin levels
Includes-feelings, abilities, moods, personality, intelligence, communication, coping with rage and stress.
Wide ranging disorders- phobias, anxiety, dementia, psychosis, addiction, mood alteration.
Behavior occurs in response to environment but how we respond may have a genetic component.
Rarely a single gene Multifactorial Affects 1 in 1,000. Twin studies & newer –SNP-single nucleotide
polymorphism pattern analysis- identify genetic contribution.
Study of nervous system and brain variation and function. Brain facts-
Brain weighs ~ 3lbs. 100 billion nerve cells (neurons)-do not divide. >1 trillion neuroglial cells- can divide(brain tumors)
Produce growth factors Involved in neuron development Neuron movement
Brain neurons form synapses with other neurons. Communication occurs via neurotransmitters. Neurons oversee sensations, perceptions, memory, and muscular
movement. Genes control production & distribution of the neurotransmitters.
Enzymes- oversee synthesis & transport of neurotransmitters across synapse presynaptic (sending) neuron postsynaptic ( receiving) neuron receptors.
Transporter proteins ferry neurotransmitters. Review neurotransmission figure.
Figure 8.1
Myelin- coats and insulates axons (neuron extensions). Speeds neurotransmission. Schizophrenia
Signal transduction-series of biochemical reactions , a cascade effect that passes information from outside the cell to inside triggering a response. Mood disorders, mental illness
Serotonin transporter mutation- Autism.
Hard to identify inherited and environmental contributors to a behavioral disorder.
Same symptoms can have different causes. Heritability-estimate (measurement) of the phenotypic
variation that is due to genes. observed phenotypic variation /expected. higher heritability %- more genetic influence.
What is normal? Range of reactions Subjective reporting-
bias behaviors can be imitated.
Table 8.1
Complex and variable trait subject to multiple genes and environmental influences and intense subjectivity
Refers to ability to reason, learn, remember, synthesize, deduce, and create.
First intelligence tests-sensory & reaction times 1904, IQ(Intelligence quotient) test developed to predict
academic success of developmentally handicapped children Stanford University modified for white, middle-class
Americans IQ is normally distributed around a mean of 100.
below 50 severe mental retardation 50-70 mild mental retardation 85-115 average above 115 above average
Correlates with success-school, work Low IQ-societal situations- poverty, H.S. dropout, high divorce,
incarceration, children out of wedlock. IQ tests- short exams
Verbal fluency, mathematical reasoning, memory, spatial visualization.
g –general or global ability in these 4 areas. Heritability increases with age; environmental effect
decreases with age-evens out. Affected by many chromosomal disorders. Gene that encodes for N-CAM ( neural cellular adhesion
molecule )– high IQ Chromosome 4- intelligence related genes.
Autism
Disorder of communication Asperger syndrome is a related disorder General population incidence < 0.1% Twin studies – 90% heritability (an estimate of
the proportion of phenotypic variation in a group due to genes).
4 – 6 major genes, up to 30 others Autism is probably several different disorders
Eating Disorders Are a Behavioral Trait
Anorexia nervosa psychological perception of obesity and intentional starvation
Bulimia psychological perception of obesity and intentional vomiting
Muscle dysmorphia psychological perception of being too small
Genes Affecting Eating Disorders
Candidate genes encode proteins that control appetite, regulate certain neurotransmitters (dopamine and serotonin)
SNP maps may identify regions that create a predisposition to eating disorders
Anorexia Nervosa
Women in U.S. have 0.5% lifetime risk
Risk of mortality is 15-21% 2.5% risk of second eating disorder 10% of cases are males Heritability of 0.5 - 0.8 Concordance
55% MZ twins 7% DZ twins
Sleeping Disorders
Without sleep animals die The function remains unclear Genetic contributions are indicated by
heritability among families and identification of genes in model systems
Twin studies indicate 4 of the 5 stages of sleep have a hereditary component
Environmental influence is great
Narcolepsy with Cataplexy
• Daytime sleepiness with tendency to rapidly fallasleep (narcolepsy) and periods of muscleweakness (cataplexy)
• 1999, first gene identified with sleep in dogs
•Problems with receptor for hypocreatin neuropeptide
•Orexin protein (signal to eat) binds to receptor
Figure 8.3
Familial Advanced SleepPhase Syndrome
Heterogeneic, but in this family, the condition is an autosomal dominant caused by a single base substitution
Figure 8.4
Drug Addiction
Compulsively seeking and taking a drug despite knowing its adverse effects
Characteristics: Tolerance the need to take more of a
drug to achieve the same effect Dependence the onset of withdrawal
symptoms with cessation of drug
Drug Addiction Brain changes that contribute to addiction are in the limbic system
Drug addiction produces stable, not transient, changes in the brain
Heritability is 0.4-0.6
Twin and adoption studies support role of genes in drug addiction
Concordance- measure of degree a trait is inherited by calculating the percentage of twin pairs in which both members express a particular trait. High concordance among identical (MZ) twins indicates a strong genetic component.
Figure 8.6
Proteins Involved in Drug Addiction
Biosynthetic pathways of neurotransmitters
Neurotransmitter reuptake transporters
Cell surface receptors
Signal transduction pathway in postsynaptic neuron
Drug Addiction
A candidate gene codes for dopamine D(2) receptor
DNA microarray studies reveal many genes whose protein products affect neurotransmission, signal transduction, and myelin deposition on neurons
DNA expressions profiles may change with addiction to different drugs
Mood Disorders
Mood disorders represent the extremes of normal behavior.
Major depressive disorder
marked by unexplained lethargy and sadness and chronic depression
Bipolar affective disorder (manic-depression) marked by depression interspersed with mania
Mood Disorders
Serotonin, a neurotransmitter, can affect mood, emotion, appetite, and sleep
Many antidepressive drugs are serotonin reuptake inhibitors (SSRIs)
Figure 8.7
Schizophrenia
Loss of ability to organize thoughts and perceptions – withdrawal from reality
Worldwide – 1% affected Typically early adult onset Progression – difficulty paying attention,
memory and learning difficulties, psychosis (delusions and hallucinations)
Schizophrenia Is a Multifactorial Trait
• Empiric risk estimates and heritability (0.8) indicate a large genetic component
• Concordance is high but a person with a schizophrenic MZ twin has a 52% of NOT developing the disease.
• Environmental associations important
• Many candidate genes and genome regions
Environmental Risk Factorsfor Schizophrenia
Table 8.3
Review
Table 8.4