Gene-Environment Interactions

I. IntroductionA. Behavior geneticsB. Genotype and 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. Gene-environment correlations1. Scarr and McCartney model2. Three different gene-environment correlations

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

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?

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

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Reaction Ranges

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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 CorrelationsThe Scarr and McCartney Model

Child’s Genes

Child’s Environment

Child’s Phenotype

Child’sGenes

Child’s Phenotype

Parent’sGenes

Child’s Environment

Gene-Environment CorrelationsThe Scarr and McCartney Model, con’t

Gene-Environment CorrelationsThe Scarr and McCartney Model, con’t

Child’sGenes

Child’s Phenotype

Parent’sGenes

Child’s Environment

Gene-Environment CorrelationsThe Scarr and McCartney Model, con’t

Child’sGenes

Child’s Phenotype

Parent’sGenes

Child’s Environment

Gene-Environment CorrelationsThree 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 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