GENERAL PSYCHOLOGY
Lecture 3
HEREDITY & THE ENVIRONMENT
Visiting Assistant PROFESSOR YEE-SAN TEOH
Department of Psychology
National Taiwan University
1
Unless noted, the course materials are licensed
under Creative Commons AttributionNonCommercial-ShareAlike 2.5 Taiwan (CC
BY-NC-SA 3.0)
HEREDITY
GENETIC FACTORS
DETERMINE ONLY AN PERSON’S
GENOTYPE (STARTING POINT),
BUT GENES DO NOT DETERMINE
HOW THE PERSON WILL END UP
(PHENOTYPE)
WHAT IS THE GENOTYPE?
Genes inherited from parents
Determines characteristics
such as height, eye color
Genotype
No 2 people have exactly the
same genotype, except
identical twins
Interacts with environment to
produce phenotype
WHAT IS THE PHENOTYPE?
Genetic expression of
individual’s physical &
behavioral characteristics
Observable & Measurable
Phenotype
Study of phenotype helps us
understand how genes &
environment interact to
influence development
E.g. Motor abilities, intellectual
skills, social behavior,
personality traits
THE GENOTYPE
THE PROCESS OF GENETIC
TRANSMISSION
WHERE THE GENES ARE
Within each cell
nucleus are
chromosomes…
 On which genes
containing the genetic
code are located
 Chromosomes are
bound by molecules of
DNA.

TRANSMISSION
MEIOSIS & SEXUAL
REPRODUCTION
Chromosome combinations occur
during the formation of sperm
and egg cells.
 Crossing over – exchange of
genes on homologous
chromosomes.
 Union of sperm and ovum = 23
male & 23 female chromosomes

THE PROCESS OF GENETIC
TRANSMISSION
MEIOSIS IN DEPTH
Process of cell division.
 23 chromosome pairs
are split/halved.
 Halving enables union
of sperm and egg.
 Result is 23 from the
sperm combines with
23 from the egg to
produce 46 for new
human being.

HOW TRAITS ARE TRANSMITTED
Since genes are located on
chromosomes, they also come in
pairs.
 Each gene occupies a position
on each half of the chromosomal
pair.
 2 identical paired genes =
homozygous
 2 different paired genes =
heterozygous
 A specific gene has alleles which
produce variations of that gene.

Wikispaces: KKPM
HOW TRAITS ARE TRANSMITTED
Expressions of heterozygous combinations:
1.Dominant – one gene will govern outcome over other
gene.
E.g. Dimples vs no dimples
2.Recessive
– allele that will affect phenotype only if it
matches allele of partner gene (inherits same recessive
allele from each parent).
E.g. Baldness only if the gene pair is homozygous for
the recessive trait.
HOW TRAITS ARE TRANSMITTED
Expressions of heterozygous combinations:
3.Codominant – both genes affect phenotype.
E.g. Blood type A + Blood type B = AB
4.Incomplete
dominance – person with 2 different
alleles will have a phenotype that’s intermediate.
E.g. Serotonin transporter gene located on
chromosome 17 can have alleles of different
length, long allele has incomplete dominance
over short.
POLYGENIC INHERITANCE
The expression of some traits is controlled by
more than one gene pair.
 Specific genetic patterns create a risk of
developing a certain trait/disease.

Example:
 Bipolar disorder and schizophrenia are much
more likely if a person inherits a certain genetic
pattern (not just one gene).
INTERACTION OF GENES
Very few traits are specified by single genes – most
traits depend on a combination of genes.
 Many behaviors or characteristics are influenced by
multiple genes.
 A gene may influence more than one trait.
 Modifier genes affect the expression of other genes.

Online Mendelian Inheritance in Man
(OMIM)
Access the website for genetic database.
GENE EXPRESSION


Whether or not a gene will be active, depends on
many factors that modify the biochemical
environment inside the cell, turning genes “on” or
“off”.
What can alter gene expression?
1. ENVIRONMENT JUST OUTSIDE THE
CELL…OTHER CELLS
Gene
Gene
Gene
2. TIMING – SOME GENES ACTIVE EARLY
VS LATE
Adulthood
Adolescence
Childhood
C. OVERALL ENVIRONMENT & BEHAVIOR
TEMPERATURE
LEVEL OF STIMULATION
Weather or climate
Engaging vs Impoverished
GENE
EXPRESSION
SOCIAL WORLD
BEHAVIOR
People you are with
Exercise triggers body
changes that activate gene
GENE-ENVIRONMENT
INTERACTION IS BI-DRECTIONAL
Gene
Expression
Environment
Experience
Bidirectional Interaction between Genetic Factors
and Context
(a) Environment & experience impacts gene
expression.
(b) Genetic factors shape what person experiences.
THE FIELD OF HUMAN BEHAVIOR GENETICS
Addresses the question
of why humans develop
in such diverse ways
Calculation of heritability
factors – estimates of
contribution of heredity
HUMAN
BEHAVIOR
GENETICS
Studies the relative
influences of heredity &
environment
Heritability factors vary
according to environment
SOME MISCONCEPTIONS OF BEHAVIOR
GENETICS….(RUTTER, 1992; 2006)
 Genes
limit potential.
 Strong genetic effects = insignificant
environmental influences.
 Genetic influences diminish with age.
 Genes regulate only static characteristics.
HEREDITY & THE ENVIRONMENT
HOW DOES THE ENVIRONMENT
RANGE OF REACTION
INFLUENCE THE EXPRESSION OF GENES?
ENVIRONMENT
GENES
RANGE OF REACTION
(GOTTESMAN, 1963; PLOMIN, 1995)
 Heredity
 It
does not rigidly fix behavior.
establishes a range of possible
developmental outcomes that may occur in
response to different environments.
 People
with different genetic make-ups have
different ranges of reaction.
 Range
of reaction is particularly useful for
understanding the variation in complex
behaviors.
EXAMPLE:


An enriched, stimulating
environment can
substantially improve a
child’s intellectual ability.
However, each child’s
genotype determines the
limits within which his/her
ability will vary.
Source: From "Genetic Aspects of Intelligent Behavior " (p. 255), by I. I.
Gottesman, in N. R. Ellis (Ed.), Handbook of mental deficiency: Psychological theory and research,
1963, New York: McGraw-Hill.
Outcome 1
Environment
A
Outcome 2
HEREDITY
Environment
B
Outcome 3
Highly aggressive
Violent
Neighborhood
Sometimes
aggressive
Aggressive
Trait
Safe, classy
nieghborhood
Less aggressive/
controlled
AN IMPORTANT INFLUENCE ON
THE GENE-ENVIRONMENT
INTERACTION…
Developmental Stage
 Critical periods: developmental stages where the
impact of the environment on development is
most significant.

Example:
Kids with PKU must be placed on a special diet
(low in phenylalanine) immediately after birth to
prevent mental retardation (Baumeister, 1967)
HOW DOES GENETIC MAKEUP SHAPE ONE’S
ENVIRONMENT?
PASSIVE
EVOCATIVE
• Parents with
certain genetic
predispositions
create home
environments that
suit the inherited
predispositions of
their children.
• Children’s
inherited
tendencies/
behaviors evoke
certain responses
from others/social
environment.
ACTIVE
• Genetic makeup
leads children to
seek out
experiences/
settings that are
compatible with
their inherited
tendencies.
• Niche-Picking
EXAMPLES….
PASSIVE
EVOCATIVE
ACTIVE
• Intelligent, well
educated parents
provide home with
books and
stimulating
conversation.
• Children’s
inherited
tendencies to be
bright & learn are
enhanced
• Babies with
inborn tendencies
to smile often will
elicit positive
response &
stimulation from
others (La
Freniere, 2000) ->
• Babies’ genetic
dispositions are
magnified, smile
more
• Niche-picking
• Children
genetically
predisposed to be
extroverted
actively seek
company & join
social activities.
• Extroversion is
enhanced.
METHODS OF STUDYING INDIVIDUAL
DIFFERENCES
1. Compare adopted children with their
biological & adoptive parents.
-
-
-
Similarity to adoptive parents = environment.
Similarity to biological parents = shared genetic
makeup.
Studies by Moffitt & Caspi, 2006; Rutter, 2006)
Comparison of biological siblings and adopted
children in same home.
2. Compare identical and fraternal twins
raised together in the same home.
-
-
If identical twins show more resemblance on a
trait than fraternal twins do = genetic influence
If both identical and fraternal twins show similar
strength of resemblance on a trait = environment
3. Compare shared & non-shared environments
-
Identical twins have more shared environments –
(i) identical genes & inherited predispositions,
(ii) similar treatment by parents,
(iii) evoke similar responses from others,
(iv) select more similar
settings/companions/activities (Scarr, 1996).
-
Fraternal twins & siblings are more likely to have
separate experiences and activities.
-
Towers et al. 2003 - similarity caused by shared
home declines with age, more niche picking.
3 PRINCIPLES OF EVOLUTION OF
BEHAVIOR THROUGH NATURAL SELECTION
(a)
(b)
(c)
There must be a variation among the
individuals within a population.
Certain of the variants must survive and
reproduce at higher rates than others.
The traits associated with this superior survival
and reproduction must be passed from parents
to offspring.
Genes
Evolution
of
Behavior
Environment/Experience
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Wikispaces: KKPM
http://kkpm.wikispaces.com/Genetics+an
d+Evolution
2012/03/17 visited
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This graph is adapted from Gottesman,1963
http://www.archive.org/details/handbookofment
aL00elli and out of copyrigh so belongs to
public domain.
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