Download From Genes to Behavior: Outline

From Genes to Behavior: Outline
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Review of Ridley
Gene-environment interactions: norms of reaction
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tanning, geckos, soapberry bugs
Violence, MAOA and Upbringing
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epigenetics
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heritability
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Ease of learning: selection shapes what we learn, and when
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Garcia: why does a reinforcer reinforce?
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What do infants attend to?
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Sensitive period learning
Discussion of Ridley
Tale of two voles: monogamous (prairie) polygynous (montane)
What makes them behave differently?
Discussion of Ridley
Tale of two voles: monogamous (prairie) polygynous (montane)
What makes them behave differently?
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Vasopressin/oxytocin: hormones promotes social bonding
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affects cells only if a receptor for it in the cell
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prairie vole has mutation (insertion) in promotor region of
receptor gene
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changes expression of gene in different parts of brain
Discussion of Ridley
Tale of two voles: monogamous (prairie) polygynous (montane)
What makes them behave differently?
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Vasopressin/oxytocin: hormones promotes social bonding
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affects cells only if a receptor for it in the cell
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prairie vole has mutation (insertion) in promotor region of
receptor gene
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changes expression of gene in different parts of brain
SO: a change in a single gene affects monogamy or polygyny!
Discussion of Ridley
Some questions:
what happens to montane vole (and mice) given prairie vole
receptor gene?
Discussion of Ridley
Some questions:
what happens to montane vole (and mice) given prairie vole
receptor gene?
they became more affiliative with their mated partners
Discussion of Ridley
Some questions:
what happens to montane vole (and mice) given prairie vole
receptor gene?
they became more affiliative with their mated partners
Do we also need an environmental signal to release vasopressin?
Discussion of Ridley
Some questions:
what happens to montane vole (and mice) given prairie vole
receptor gene?
they became more affiliative with their mated partners
Do we also need an environmental signal to release vasopressin?
Sex → release of vasopressin → male gets “addicted” to his mate.
So environment matters, but a simple response
How to think about genes and environment: Norms of
reaction
norm of reaction:
expression of a genotype in different environments
Response is shaped by selection, so also evolved “human nature”
Norms of reaction: sex ratio in leopard geckos
Leopard gecko nature:
more males to be born when the temperature is high
Norms of reaction: Mate-guarding in Soapberry bugs
When is it adaptive for bugs to mate-guard?
Norms of reaction: Mate-guarding in Soapberry bugs
When is it adaptive for bugs to mate-guard?
Gene-culture interaction: Violence, MAOA and Upbringing
Violence, MAOA and Upbringing: two reaction norms
NOTE: has not always been replicated
Epigenetics; How the environment affects gene expression
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humans are just under 99 percent genetically identical to
chimpanzees
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Difference is in which genes are switched on or off in
development
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liver and skin cells contain same genes; not all expressed.
Why?
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Epigenome: chemical markers and switches on chromosome
that prevent expression.
One epigenetic marker is a methyl group (CH3) attached to
DNA, silences gene
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A gene silenced like that is said to be “imprinted”
The epigenome is affected by the environment: software to
DNA hardware
Epigenetics: Diet, BPA and the agouti mice
Randy Jirtle and the agouti mice:
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agouti mice carries gene that makes them ravenous, diabetic,
and yellow
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most offspring like their parents
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unless fed “special diet” rich in methyl-donors (onions, garlic,
beets)
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then they had the same gene, but looked brown and healthy
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some of those chemicals are in vitamins for pregnant women
too
What does exposure to BPA do to the agouti mice?
Epigenetics: BPA and the agouti mice
environmental influences affect gene expression throughout life
Epigenetics: Behavior affects the epigenome
Michael Meaney: 2 kinds of mother rats
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nurturing rat moms (licked babies) had brave, calm babies
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neglectful rat moms (didn’t lick) had nervous, fearful babies
what is going on in the rat brain?
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licking releases serotonin, activates serotonin receptors in
hippocampus
licked rats have bigger hippocampi, less cortisol
rats have same genes, different methylation patterns in
hippocampus
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is it reversible? yes
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Trichostatin (similar to valproate, mood stabilizer) given to
adult rats could reverse epigenetic signals
behavior can influences gene expression throughout life
Epigenetics: What about people?
Parenting affects children (in low birthweight babies)
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adults with poor relationship with mother: small hippoampi
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adults with good relationship with mother: large hippoampi
What about grandchildren?
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Pembry studied 200 yrs crop yields in Sweden; food
availability fluctuated a lot
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grandfathers who were young teens in good times had
grandsons with diabetes
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grandmothers who were babies in good times had
granddaughters with diabetes
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What happened? sperm formed in teen years, eggs in utero or
as infants
A brief note on heritability
LESSON THUS FAR:
WHEN TALKING ABOUT AN INDIVIDUAL, cannot separate
genes from environment
BUT, WHEN TALKING ABOUT A POPULATION:
Geneticists do separate variation due to genes and environment
heritability =
proportion of phenotypic variance due to genetic variance
1. note: heritability only applies to a population
2. more environmental variance lowers heritability
Ease of learning
Learning biases: Another view of gene-environment interactions
1. Genes affect what you learn easily
2. Some things are easy to learn, others hard
3. Genes affect what you attend to. . .
4. And what you attend to is what you are likely to learn
Ease of learning: Garcia’s experiments
Ease of learning: Attention in infants
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What you attend to is what you learn: faces are important
Ease of learning: Attention in infants
Eyes are especially salient. . .
Ease of learning: Attention in infants
...Especially when those eyes are looking at you.
Summary
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Genes don’t do anything unless they are expressed
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Epigenetic switches control gene expression
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Environment and behavior affect that expression (agouti mice,
upbringing)
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Reaction norms summarize how a genotype is expressed in
different environments
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Reaction norms – the response of the gene – is genetic
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Genes also affect learning and attention in adaptive ways