Transcript genetic polymorphisms

Chapter 2
 How
do nature and nurture, person and
environment, individual and context
interact to produce behavior?
 How nature or nurture is really nature and
nurture
 Genetic variants provide one piece of the
puzzle in explaining variation in human
behavior
Disorder/Maladaptive
Behavior
Environmental Risk
Genetic Risk
 Virtually
all behaviors are in part caused
by genetic factors but this does not mean
they are unchangeable
 Upwards of 90% of the causal variance of
autism is attributable to genetic factors.
 However, early intervention and intensive
treatment—environmental factors under
the control of social work staff—can
dramatically reduce the problem
symptoms of autism.
 Clients
with actively involved parents
and strong family and community
supports constitute additional
environmental strengths that can
surmount various disabilities.
 In other words, social workers have a host
of clients who, they sense, present with
some balance of biological, genetic, or
neurological risks (and assets) coupled
with environmental risks (and assets).
Nonshared
Environment
Heritability
Shared
Environment
 diathesis-stress
model
• Persons who are at genetic risk for some
disorder or condition are most sensitive to the
stressors created by environmental risk
 natural
selection
• Characteristics that facilitate the survival and
reproductive success of an organism persist
whereas characteristics that do not facilitate the
survival of the species desist.
 genetic
drift
• Genetic evolution that is random and neutral
 Mendelian
disorder
• An inherited condition caused by a single
genetic mutation
 multifactorial
phenotypes
• phenomena caused by genes, environments, and
their interaction
 heritability (h2)
• a population statistic indicating the proportion of
variance in a phenotypic (or outcome) trait in a
population that is attributable to genetic factors
 shared environment (c2)
• common environmental exposure that relates usually
to within-family characteristics
 nonshared environment (e2)
• source of environmental variation relates to
circumstances that are unique to the individual even
within the same family
 polygenic
• a trait or behavior caused by many genes
 pleiotropic
• individual genes that are associated with
multiple phenotypes
 alleles
• variants of a single gene
 genetic
polymorphisms
• genes with different forms within a population
 Personality
• The trait of novelty/sensation seeking was the
first to be linked to a specific gene, the
dopamine receptor known as DRD4.
• The 7-repeat allele of DRD4 has been shown to
be associated with novelty/sensation-seeking
personality traits

Associated with high levels of the personality trait
of novelty seeking, which characterizes those who
are impulsive, exploratory, fickle, excitable, and
quick-tempered as opposed to reflective, rigid,
loyal, stoic, slow-tempered, and frugal
 Personality
(Continued)
• 7R allele of DRD4 has been linked to alcohol
abuse, binge drinking, and substance abuse
generally
• The gene is also associated with ADHD
 Diagnosis
Heritability Range
 ADHD
60–90%
 Alcohol Dependence 50–60%
 Anxiety Disorder
40–50%
 Major Depression
40%
 Manic-Depression
60–85%
 Schizophrenia
70–85%
 Biosocial
development starts at an early age
 Maternal substance use is a direct,
pernicious way that parents can cause
neurological problems for their children.
 Environmental risks, or pathogens, also
exist in indirect broader contexts as well.
For example, many toxins found in the
environment have been shown to affect
brain development and behavior.
 It
is important to note that heritable
conditions are not exclusively related to
antisocial behaviors, but also to other
forms of maladaptive or unhealthy
behaviors, such as obesity.
National Institute of Child Health and Human
Development Study of Early Child Care and
Youth Development found that children who were
unable to delay gratification at age 4 were
significantly more likely than children who could
delay gratification to be overweight at age 11.
 This relationship withstood controls for the
child’s body mass index at age 4, maternal
expectations of the child’s ability to delay
gratification for food, and mother’s weight status,
although the latter was also an important
variable.

 Neurogenetic
factors continue to influence
behavior during adulthood
 A study of predatory and reactive
murderers found that affective or reactive
murderers had reduced prefrontal activity
and increased subcortical (limbic) activity
compared to controls.
 Predatory
murderers had similar
prefrontal activity to controls but
excessive subcortical activity.
 These findings suggest that cold blooded
killers are able to exercise
neurocognitive control of their instincts
despite excessive limbic activity,
whereas hot-blooded killers are not.
The diathesis-stress model asserts that genetic
risks are most sensitive to environmental risks for
disorders and maladaptive behaviors.
 A cell to society approach advances a biosocial
framework where nature, nurture, and their
interaction produce behavior.
 Natural selection and neutral, random mutation
are responsible for evolutionary changes in the
human genome.
 The central dogma of molecular biology
articulates the ways that DNA is transcribed into
RNA and ultimately translated into proteins and
enzymes.

 An
inherited condition caused by a
single genetic mutation is a Mendelian
disorder, and these follow the laws of
simple inheritance.
 Variance in behavior is attributable to
three sources: heritability, shared
environment, and nonshared
environment.
 Behaviors that are caused by genes,
environments, and their interaction are
known as multifactorial phenotypes.
 Genetic
polymorphisms are genes that have
different forms within a population, and the
individual variants are called alleles.
 More than half of human genes are
expressed in the brain, and genetic
variation gives rise to variance in neural
substrates or pathways that relate to
cognitive and behavioral functioning.
 Gene–environment interactions occurring
during gestation, infancy, childhood,
adolescence, and adulthood shape human
behavior.