Download heritability

Unit 4: Mods 6-11 & Barron’s 9: Nature, nurture, and human development
Mod 6 essentials: Behavior genetics and evolutionary psychology
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What distinguishes behavior geneticists from other kinds of psychologists?
Define DNA, chromosomes, gene, and genome.
What conclusions have behavior geneticists drawn by studying identical twins,
fraternal twins, and adopted children?
How have studies on temperament contributed to our understanding of nature
and nurture?
What is heritability?
What are molecular genetics and epigenetics and how are they contributing to
psychology in the 21st c.?
What is the main focus of evolutionary psychologists?
What explanations do evo. psychs. give for human sexuality behaviors?
What are the criticisms of the evolutionary perspective?
1. What distinguishes behavior geneticists from other kinds of psychologists?
•They look at both nature and nurture causes of behaviors!!
•They are mostly interested in answering: What causes us to be unique, different than
one another?
• Behavior geneticists are interested in how genes AND
environments, from womb to tomb, influence our behaviors AND
create individual differences
– Womb
• effects of prenatal nutrition on brain and body development
• exposure to teratogens (environmental toxins that reach
developing fetus) that create deformities, mutations
• exposure to virus, parasites if mom gets them while preg.
– Lifetime outside the womb
• relationships, interactions with people
• interactions with the world and experiences
• trauma, accidents, diseases
2. The language of geneticists
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DNA : the chemical components of
chromosomes
Chromosomes: Human has 23 pair—they
consist of genes we inherit from our mom
and our dad
Genes: DNA sequences on chromosomes
that help determine human characteristics
and govern physiological processes—
humans have approx. 30,000 genes
Allele: ½ of a gene pair—1 exists on each
paired chromosome
Human genome is the map of 30,000
possible genes existing in human kind
Human karyotype (# and appearance of
chromosomes in a species)
Word choices
alleles
chromosomes
DNA
genes
genome
karyotype
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Genotype: The genetic
constitution of an individual.
– Unless you have an identical
twin, you have a unique
genotype made up of half of
dad’s and half of mom’s
chromosome
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Phenotype: The set of observable
characteristics of an individual
resulting from the expression of
genes and/or interaction of its
Punnett square: Diagram
genotype with the environment
used to predict gene
– height –influenced by diet
expression based on
– eye color influenced by
dominant/recessive genes
dominant allele
– fingerprint influenced by
In order to express itself, a recessive gene
environmental factors in
(lower case a) must be paired with another
womb of developing fetus
recessive gene! In above Punnett square,
what is likelihood of baby having the “a”
recessive disorder?
25%!
Genetic variation from the norm:
Mutations on genes, too many chromosomes, or not enough chromosomes!
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– Down’s syndrome—trisomy 21 (baby has 3 copies of 21st chromosome (1 in 800 live
births)
– Klinefelter (XXY) & Turner Syndrome (X)
Recessive disorders (means you need 2 copies of the gene, 1 from mom, 1 from dad, to
get disease. Neither mom nor dad needs to have disease—could just be a carrier of
dormant gene!)
– cystic fibrosis--hick, sticky mucus to build up in the lungs, digestive tract, and other
areas of the body
– PKU-- body cannot process the amino acid phenylalanine which is found in many
foods—if eaten, can cause retardation
– albinism--defect of melanin production that results in little or no color (pigment) in
the skin, hair, and eyes.
– Tay-Sachs disease--fatal
Dominant disorders (means you only need1 copy of the gene from either dad or mom to
get disease and disease is observable in mom or dad)
– Huntington chorea—defect on gene; 4 neurodegenerative disorder
– achondroplastic dwarfism—bone growth disorder due to mutation on gene
– polydactyly—extra fingers or toes!
What is heritability?
heritability: the extent to which observed differences between 2 individuals can
be attributed to their genetic differences
Heritability range = 0.0 to 1.0
The lower the number, the more we can attribute difference between individuals
to differences in their nurture (environments, experiences)
The higher the number, the more we can attribute the difference between
individuals to differences in their differences in genes
BIG IMPORTANT IDEAS:
1.Heritability CANNOT be used to tell what % of any one individual’s traits or behaviors are
caused by nature or nurture!! They are used to express what % of variation we see between
people is due to genetics
Example
If happiness is 50% heritable, it does not mean that Joe’s happiness level is 50% determined
by his genes and 50% determined by environment. It DOES mean that genetics influence 50%
of the differences in happiness we see between him and another person.
2.If identical twins show difference in IQ, then we would say the heritability of IQ is 0 This is
because the difference in their IQ MUST be attributable to environment since they have
identical genes!
Classic longitudinal experiment on self-discipline: The marshmallow test
•Dr. Walter Mischel of Stanford University
•Tempt 3-4 year-olds with a marshmallow
•Tell them that they may eat it now OR wait 15-20 minutes while
marshmallow is in front of them and receive a second if they do not eat it
Video
Why does self-discipline matter?
Direct correlation between being able to delay gratification
and future academic success, popularity, success in getting
over frustrations and challenges, saying “no” to temptations
6. What are molecular genetics and epigenetics and how are they used in the field of
psychology?
• Molecular geneticists study the ways specific genes/groups of
genes shape behavior
– e.g. Look for a genes that might cause homosexuality or
schizophrenia or ADHD or obesity or bipolar
• Epigeneticists study the way our genes become “modified” by
our interaction with our environments
– The genes chemical structures do not actually become
modified, BUT the expression of the genes does due to
physiological changes at the DNA level that allow genes to
“turn on” or “turn off”
– In sum, your epigenome is chemical tags on your DNA that
are created as you interact with the environment. These
tags switch on or off your genes and can shape your
behaviors!
Epigenetics: The latest and greatest in science to explain how nurture
acts on what nature endows!
Epigenetics videos
• Video link 1 (5 min) How environment in womb can make identical
twins different
• Video link 2 (5 min) Rat experiments—lick a rat pup!!
7. What is the main focus of evolutionary psychologists?
• What makes us alike as humans and how do our genes drive our
behaviors?
– In contrast with molecular geneticists, evolutionary look at how
genes explain male or female behavior or adult or child behavior
rather than the behavior of the individual
• Everything is about natural selection and survival of the fittest!!
8. What explanations do evo. psychs. give for human sexuality behaviors?
• Who wants sex more often? Survey says...
– MEN MEN MEN!
• Who thinks about sex more often? survey says...
– MEN MEN MEN!
• Who associates sex with affection and cuddling? Survey says...
– WOMEN, WOMEN, WOMEN!
• Who has no problem with casual sex? survey says...
– men men men
• Who falls in love after an orgasm?
– WOMEN, WOMEN, WOMEN!
• Who is sexually charged by visual stimuli?
– men men men!
WHY?
More on sexuality...
What do women find attractive in
mates (men)?
• Taller than themselves
• muscular
• wider face
• risk takers
• dominant
• affluent
• protectors
• good saliva *
What do men find attractive in
women?
•youthful looking
•smooth skin
•big breasts
•wide hips
•a woman in heat*
WHY??