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Gene-Environment Interactions
I.
Introduction
A. Genotype
B. Phenotype
II. Genes, the organism, and the environment
A. What is a gene-environment interaction?
B. Waddington’s cannalization principle
C. Gottesman’s Range Of Reaction principle
1. Genetic constraints on individuals
2. Problems with range of reaction
3. Kinship studies
D. Feedback in gene-environment interactions
1. Scarr and McCartney model
2. Three different gene-environment
interactions
a. Passive gene influences
b. Evocative gene influences
c. Active gene influences
E. The ahistorical-historical dimension
III. Questions about gene-environment interactions
A. Is there a developmental program?
B. Do genes determine the phenotype?
C. Do genes determine capacity?
D. Do genes determine tendencies?
What do we mean by gene – environment
interactions?
Variations in any level of the environment can have an
impact on the development of the organism
• Experiments on the Himalayan rabbit
• Studies of fur color
How do we study gene-environment interactions?
• Keep environments of different genotypes
constant
• Keep genotype constant while varying the
environment
Waddington’s canalization principle
Although both influence development, genes might
influence some attributes more than others
• Conrad Waddington
• Canalization - Cases in which genes restrict
development to a small number of outcomes
• Example – Babbling in infants
• Canalization and critical periods
Implications of canalization
• Multiple pathways of development
• Some circumstances, genes may limit the extent
to which environments can influence
development
Gottesman’s Range of Reaction Principle
Individual genotypes might operate in ways to restrict
development or constrain outcome
• Range of reaction principle:
• Genotype, or genetic structure, sets the
limits on the range of possible phenotypes
that a person might display in response to
different environments:
• Example: Intellectual development in children
The Range of Reaction Principle
Intelligence Quotient
160
Reaction Ranges
A
120
A
B
80
B
C
C
40
0
Restricted
Average
Type of Environment
Enriched
Gottesman’s Range of Reaction Principle
Individual genotypes might operate in ways to restrict
development or constrain outcome
• Range of reaction principle:
• Genotype, or genetic structure, sets the
limits on the range of possible phenotypes
that a person might display in response to
different environments:
• Example: Intellectual development in children
• Generally, a statement about the interplay
between environment and heredity
Problems with range of reaction principle
• Issues in terms of how to investigate principle
• Issues in terms of finding genetically identical
individuals.
Kinship studies:
• Studies in which members of same biological
family compared to see how similar in
attribute(s)
• Monozygotic twins – genetically identical
• Dizygotic twins, siblings – genetically similar
• Half siblings
The Scarr and McCartney Model
Child’s Genes
Child’s
Phenotype
Child’s
Environment
The Scarr and McCartney Model, con’t
Child’s
Genes
Parent’s
Genes
Child’s
Phenotype
Child’s
Environment
The Scarr and McCartney Model, con’t
Child’s
Genes
Parent’s
Genes
Child’s
Phenotype
Child’s
Environment
The Scarr and McCartney Model, con’t
Child’s
Genes
Parent’s
Genes
Child’s
Phenotype
Child’s
Environment
Three Different Genotype-Environment
Interactions
Passive gene influences
• Parents contribute to development in two ways:
• Provide genetic material
• Structure environment socially and
emotionally
• Because environments provided/created by
parents depend on their genotype,
environments will be generally matched to
children’s genotype
Evocative gene influences
• Child’s heritable characteristics affect behavior
of others towards child
Active gene influences (niche picking)
• Environments children prefer and seek out
those that are most compatible with genetic
predispositions
Questions about
Genotype-Environment Interactions
Is there a developmental program?
• Analogy between genetic code and computer
program
Do genes determine the phenotype?
• Once genotype is fixed, phenotype is
determined
Do genes determine capacities?
• Genotype sets the absolute limits on the nature
of the phenotype
Do genes determine tendencies?
• Genotype determines a general tendency
toward a particular phenotype
• Example – the genetic contribution towards
excitability is a tendency to get excitedv