Transcript Human Genetics

Human Genetics
Concepts and Applications
Tenth Edition
RICKI LEWIS
8
Genetics of
Behavior
PowerPoint® Lecture Outlines
Prepared by Johnny El-Rady, University of South Florida
Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Objectives
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Identify the physical basis of behavioral traits in
the brain.
Discuss the difficult in analyzing behavioral traits
and disorders
Explain how genetics may be used to
understand behavioral disorders
Discuss the genetics and environmental
influences on eating, sleep, intelligence,
addiction, mood, schizophrenia and autism
Explain relations between some of them
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Genes and Behavior
Behavior:
- a continuum of emotions, moods,
intelligence, and personality
- occurs in response to environmental factors
how we respond has genetic underpinnings
Behavioral genetics considers nervous
system function and variation
- Including mood and mind
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The Human Brain
The human brain weighs about 3 pounds
- Consists of neurons and supportive and
nurturing cells called neuroglia
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Neurons communication:
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Synapses
neurotransmitters
Genes control the production and
distribution of these chemical signals
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Neurotransmission
Genes controlan la
produccion y distribución de NT
Sinapsis
Neurotransmisores
Canales
Bombas
Mielina
Enzimas
Figure 8.1
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Behavioral Genetics
Uses empirical risk, twin studies, and
adoption studies
Association studies with SNPs and analysis
of specific mutations that are present in
individuals with the behavior
Genetic studies of behavioral disorders are
challenging traditional psychiatric
classification
- These disorders may lie on a continuum
with many genes having input
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Porque es difícil analizar
comportamientos:
-Sintomas de diferentes
síndromes se solapan
-Participantes pueden dar
información biased o sea
prejuiciada
-Se puede imitar
comportamientos (hermanas
con anorexia)
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Eating Disorders
In the US, 5-10 million people have eating
disorders
- About 10% are male, both affected
Twin studies reveal a heritability ranging
from 0.5-0.8
Genes whose products control appetite or
regulate certain neurotransmitters may
predispose to eating disorders
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Eating Disorders
Anorexia nervosa – Psychological perception of
obesity and intentional starvation
-Heredability 0.5-0.8
Bulimia – Psychological perception of obesity and
intentional vomiting
Muscle dysmorphia – Psychological perception
of being too small
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Eating Disorders
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were always associated with females, risk
estimates exclude males
twin studies reveal a considerable genetic
component: heredability 0.5-0.8
If they recurs in siblings, are difficult to interpret:
its genetic or is imitation?
Genes that encode proteins that control apetite ,
serotonin, dopamine (table 7.7)
Four chromosomal regions with genes that are
active in the part of the brain that regulates eating
behavior
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Leptin and Associated Proteins
Leptin is a protein hormone produced by fat
cells
- Acts on the brain to decrease appetite
Ghrelin is a peptide hormone produced in
the stomach
- Responds to hunger by increasing
appetite
These and other hormones are important for
general weight regulation
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Leptin and Associated Proteins
Table 7.8
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Sleep
Without sleep animals die
Twin studies indicate 4 of the 5 stages of
sleep have a hereditary component
- The fifth stage, REM sleep, is
associated with dreaming and so reflects
input of experience more than genes
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Narcolepsy with Cataplexy
Daytime sleepiness with tendency to rapidly fall
asleep (narcolepsy) and periods of muscle
weakness (cataplexy)
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The genetic basis was
first identified in dogs,
then humans
Polygenic, requiring and
environmental trigger
More common in certain
families, suggest a
genetic component
Hypocretin/orexin
Figure 8.3
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Familial Advanced Sleep Phase Syndrome
A disorder characterized by a very unusual sleepwake cycle
Affected members of a large family enabled
researchers to identify the first “clock” gene in
humans
- circadian pacemaker: two clusters of neurons,
express clock genes in response to light or dark
stimuli
- The period gene enables a person to respond
to day and night environmental cues
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Familial Advanced Sleep
Phase Syndrome
A pedigree of the autosomal dominant form of the
disease
- 7:30pm fall
asleep
- 4:30 am
awaken
suddenly
- period mutated
in chromo 2
- Prevent a
phosphorilation
event
Figure 8.4
Figure 8.4 16
Intelligence
A complex and variable trait subject to
multiple genes, environmental influences,
and intense subjectivity
Refers to the ability to reason, learn,
remember, synthesize, deduce, and create
The IQ (intelligence quotient) test was first
developed in France in 1904
- To predict academic success of
developmentally disabled children
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The IQ Test
Was later modified at Stanford University to
assess 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 intelligence
▪ Above 115 = Above average intelligence
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IQ has been a fairly accurate predictor of
success in school and work
- 100 is average
- 66% of people 85-115
- 3% with intellectual
disability
- Low IQ predicts fairly
well success in school
and work
- Low IQ also relates to
poverty, divorce rate,
failure to complete high
school, incarceration,
child out of wedlock
- Opportunity =
intelectual development
Figure 8.5
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IQ tests verbal fluency, mathematical reasoning, memory,
and spatial visualization ability
The “g” value measures a general intelligence factor that
represents the inherited portion of IQ
The environment has less of an influence on IQ as a person
ages
High heritability
Several
chromosome
disorders affect
“intelligence”
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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
Evidences is mounting that genes play a role in
making some individuals prone to addiction21
Drug Addiction
Heritability is 0.4-0.6
- Twin and adoption studies support role of genes
in drug addiction
Drug addiction produces long-lasting changes in the
brain
Brain changes that contribute to addiction are in the
limbic system
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The Events of Addiction
Figure 8.6
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Proteins Involved in Drug Addiction
Enzymes involved in biosynthetic pathways of
neurotransmitters
Neurotransmitter-reuptake transporters
Cell-surface receptors
Members of signal transduction pathways in
postsynaptic neuron
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Drugs of Abuse
Abused drugs are often derived from plants
- Cocaine, opium, and tetrahydrocannabinol
(THC), the main ingredient in marijuana
- These chemicals bind receptors in human
neurons
Endorphins and enkephalins are the human
equivalents of opiates
- Are pain relievers
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Candidate Genes for Drug Addiction
Nicotine binds a receptor that normally binds
acetylcholine, causing dopamine release and
pleasure
Candidate genes for addiction include those that encode:
- The dopamine D(2) receptor
A1 alele: overrepresented in alcoholism and others
- The nicotine receptor parts
Variants of two parts: desire to smoking after first
cigarrette
- The protein neurexin-1, which ferries nicotinic
receptors to neuron’s surface
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Mood Disorders
Mood disorders represent the extremes of
normal behavior
The two most prevalent are:
- Major depressive disorder = Marked by
unexplained lethargy, sadness, and
chronic depression
- Bipolar affective disorder = Marked by
depression interspersed with mania
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Major Depressive Disorder
Affects 6% of the US population, more
women than men
A likely cause is a deficiency of the
neurotransmitter serotonin, which affects
mood, emotion, appetite, and sleep
Many antidepressant drugs are selective
serotonin reuptake inhibitors (SSRIs)
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Major Depressive Disorder:
SSRIs: seletive serotonin re-uptake inhibitors
Figure 8.7
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Bipolar Disorder
Also called manic-depression
Affects 1% of the population
Weeks or months of depression alternate with periods of
mania (out of character behaviour)
Associated with several chromosome sites
Its genetic roots are difficult to isolate
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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)
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Schizophrenia
A heritability of 0.8 and empiric risk values indicate
a strong genetic component for schizophrenia
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Schizophrenia
Dozens of genes may interact with
environmental influences to cause this
disease
One powerful candidate is infection during
pregnancy
- Prenatal exposure to the influenza or
herpes viruses
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Autism
Autism is a spectrum of disorders
- Characterized by loss of language,
communication, and social skills,
beginning in early childhood
- Seizures and mental retardation may occur
Autism affects 3-6 children out of every 1,000
- It strikes four times as many boys as
girls
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Autism
More than 30 genes so far have been
associated with autism
Two genes in particular may finally explain
how autism develops
- They encode the cell adhesion proteins
neurexins and neuroligins
- These proteins strengthen synaptic
connections in neurons associated with
learning and memory
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Understanding Autism
Autism may arise from failure of synapses to form
that enable a child to integrate experiences
Figure 8.9
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Figure 8.10
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