Transcript Document

Gene-Environment Interactions
I.
Introduction
A. Behavior genetics
B. Genotype and 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. Gene-environment correlations
1. Scarr and McCartney model
2. Three different gene-environment correlations
a. Passive gene influences
b. Evocative gene influences
c. Active gene influences
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?
Gene-Environment Interactions
Introduction
Behavior genetics
• Contributions of nature and nurture to human traits
• Polygenetic traits
• The question of “how much”
Genotype and Phenotype
• Genotype
• One’s genetic endowment
• Constant over lifetime
• Phenotype
• Observable characteristics of individual
• Emerges through interactions with genotype and
environment
Genes, the Organism, and the Environment
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
• Ex, motor development and babbling
• Canalization and critical periods
Implications of canalization
• Ensures child development under range of conditions
• Promotes survival
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
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
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
Gene-Environment Correlations
The Scarr and McCartney Model
Child’s Genes
Child’s
Phenotype
Child’s
Environment
Gene-Environment Correlations
The Scarr and McCartney Model, con’t
Child’s
Genes
Parent’s
Genes
Child’s
Phenotype
Child’s
Environment
Gene-Environment Correlations
The Scarr and McCartney Model, con’t
Child’s
Genes
Parent’s
Genes
Child’s
Phenotype
Child’s
Environment
Gene-Environment Correlations
The Scarr and McCartney Model, con’t
Child’s
Genes
Parent’s
Genes
Child’s
Phenotype
Child’s
Environment
Gene-Environment Correlations
Three types of correlations
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
Environmental Influences
on Gene Expression
Heredity as being prioritized
• Canalization, range of reaction, gene-environment
correlations
• Driven by genetics
• Problems with the supremacy of the genes
Bidirectional gene and environment effects
• Genes affect behavior, and behavior effects genes
• The epigenetic framework
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