Unit 3C - School District of Cambridge
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Transcript Unit 3C - School District of Cambridge
Intro
What causes our striking diversity and also our
shared human nature?
How much are human differences shaped by our
differing genes?
How much are human differences shaped by our
environment?
Unit3C tells the complex story of how our genes
(nature) and environments (nurture) define us.
Behavior Genetics: Predicting
Individual Differences
Behavior Geneticists: study our differences and
weigh the effects and interplay of heredity and
environment
Jaden Agassi: tennis talent because of genes or tennis
environment?
Behavior Genetics: Predicting
Individual Differences
_______________: threadlike structures made of
DNA molecules that contain genes
______: complex molecule containing the genetic info
that makes up the chromosomes
__________: small segments of giant DNA molecules,
heredity
Genes: Our Codes for Life
Each human cell contains ___ total chromosomes
___ donated from your mother’s egg
___ donated from your father’s sperm
Each chromosome is paired up with a partner,
and each chromosome pair contains thousands
of genes, which also occur in pairs.
Sometimes a member of a pair has a louder voice,
always expressing itself and masking the other,
different, member of the pair…this is a dominant
gene.
A recessive gene is one that is masked when the
paired genes are different.
Behavioral Genetics
Every other human is close to being your identical
twin -- _____% the same
Genome: complete instructions for making an
organism
Consists of all the genetic material in that organisms
chromosomes
Slight variations from common pattern give us clues to
our uniqueness (why one has cancer, tall, shy)
Genotype refers to a person’s genetic makeup
Phenotype refers to the ways in which a person’s
genotype is manifested in observable characteristics.
Identical vs. Fraternal
Twins
Identical Twins: develop from a single fertilized egg
that splits in two
Genetically identical(human clones)
However:
They don’t always have the same number of copies of
those genes (why one may get sick)
1 in 3 don’t share placenta (one may have more
nourishment)
Identical vs. Fraternal
Twins
Fraternal Twins: develop from separate fertilized
eggs
Share fetal environment but are genetically no more
similar than ordinary brothers & sisters
Separated Twin Studies
2 Jim’s: woodworking, Chevy, Nascar, Miller Lite,
son named James Alan (Allan), Dog named Toy,
Migraines, High Blood Pressure, Chain smoking,
Personality, Intelligence, Heart Rate, Brain Waves
Oskar & Jack:
One raised Catholic Nazi
One raised as a Jew in the Caribbean
Similarities: spicy food, fall asleep in front of tv, flushed
toilet before using it, rubber bands wrist, dipped toast in
coffee, physical attributes, attitudes, interests, fears
http://www.youtube.com/watch?v=Wd5Y3-F79LY
Separated Twin Studies
Criticisms of twin studies:
.
.
.
Separated Twin Studies
Criticisms of twin studies:
If any two strangers were to spend hours comparing
their behaviors and life history, they would discover
many coincidental similarities
People with similar economic and cultural
background (like many separated twins) exhibit many
similarities
Many separated twins met years before they were
tested
Biological vs. Adoptive
Relatives
Behavior geneticists also look at how:
Genetic relatives (biological parents & siblings) and
environmental relatives (adoptive parents & siblings)
impact development
For any trait, we can ask whether adopted children are
more like:
Biological parents who contributed genes (nature)
Adoptive parents who contributed home environment
(nurture)
What do you think will have a greater impact?
Biological vs. Adoptive
Relatives
Findings: people who grow up together, whether
biologically related or not, do not much resemble
one another in personality
Extraversion/Agreeableness: adoptees are more
similar to their biological parents
Compare to your siblings!
Environment shared by a family’s children has
virtually NO discernible impact on their
personalities
Link between heredity and development of
personalities
Biological vs. Adoptive
Relatives
Why are children in the same family so different?
Why does shared family environment have so
little effect on children’s personalities?
.
.
.
Heritability
Using twin and adoption studies, behavior
geneticists can mathematically estimate, the
heritability of a trait
Heritability: variations among individuals that we can
attribute to their differing genes
If all schools were of uniform quality, all families equally
loving, and all neighborhoods equally healthy, then
heritability would increase because differences due to
environment would decrease
Heritability
If heritability of intelligence is 50%
Does that mean that your intelligence is 50% genetic?
__________
Genetic influence explains 50% of the observed
variation among people
Heritability refers to the extent to which differences
among people are attributable to genes.
Nature vs. Nurture
Humans have enormous adaptive capacity
Person #1, barefoot = callused feet (biological
adaption)
Person #2, shoes = tenderfoot
Differences obviously from ______________
Genes & Environment work together
Genes respond to environments
Nature vs. Nurture
Interaction between genes and environment tell us
genes are self-regulating
Genes do not lead to the same result no matter the
context, genes react
Example: Butterfly that changes colors due to changes in
temperature in various seasons
People with identical genes but differing experiences
therefore have similar though not identical minds
Nature vs. Nurture
At least one known gene will, in response to major
life stresses, code for a protein that controls a
neurotransmitter involved in depression
By itself, the gene doesn’t cause depression
What else would be an influence?
Human differences result from both genetic and
environmental influences
Gene-Environment
Interaction
Interaction: interplay that occurs when the effect of
one factor (environment) depends on another
factor(heredity)
1.) Environments trigger gene activity (depression)
2.) Certain traits evoke significant responses in others
(impulsive student evokes angry response from
teacher)
Our genes affect how people react to and influence us =
possible changes in our behavior
Gene-Environment
Interaction
Good looks will get you that job, promotion and
raise
Review
How have heredity and environment influenced
who you are today?