Gene-Environment Interactions

I. IntroductionA. Genotype B. Phenotype

II. Genes, the organism, and the environment A. What is a gene-environment interaction?B. Waddington’s cannalization principleC. Gottesman’s Range Of Reaction

principle 1. Genetic constraints on individuals2. Problems with range of reaction3. Kinship studies

D. Feedback in gene-environment interactions1. Scarr and McCartney model2. Three different gene-environment

interactionsa. Passive gene influencesb. Evocative gene influencesc. Active gene influences

E. The ahistorical-historical dimension

III. Questions about gene-environment interactionsA. 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

T y p e o f E n v iro n m en t

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1 2 0

1 6 0

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R estric ted A v e rag e E n rich ed

Reaction Ranges

A

B

C

A

B

C

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 Environment

Child’s Phenotype

The Scarr and McCartney Model, con’t

Child’sGenes

Child’s Phenotype

Parent’sGenes

Child’s Environment

The Scarr and McCartney Model, con’t

Child’sGenes

Child’s Phenotype

Parent’sGenes

Child’s Environment

The Scarr and McCartney Model, con’t

Child’sGenes

Child’s Phenotype

Parent’sGenes

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 aboutGenotype-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