Download Behavioral Genetics: Predicting Individual Differences

Behavioral Genetics: Predicting
Individual Differences
Module 14
Genes: Our Codes for Life
• Chromosomes are long twisted strands
of deoxyribonucleic acid (DNA) found in the nucleus of the cell
• Humans have 23 pairs of chromosomes
• DNA is the chemical basis of heredity and carries instructions
• DNA code carried on each chromosome is arranged in thousands of
segments called genes.
• Genes are the basic unit of heredity
– Complex traits are formed from different combinations of genes
– Can be activated by environment
Expressing Genes: Dominant & Recessive
• Genotype—Set of genes you’re born with
• Phenotype—traits that are expressed/displayed (influenced by genes &
environmental factors
• Dominant genes—will always be expressed if present
• Traits such as freckles, dark eyes, dark hair, and dimples are referred to as
dominant characteristics because they require only one member of a
gene pair to be dominant for the trait to be displayed
• Recessive genes—will expressed only if paired with an identical recessive
gene. Will not be expressed if paired with a dominant gene.
• We inherit from our biological parents a genetic potential, the expression of
which can be influenced by environmental conditions.
Characteristic
Dominant
Recessive
Eye color
Brown
Grey, blue
Hair
Dark
Curly
Light
Straight
Hands
Extra fingers
5 fingers
Limb dwarfing Normal limbs
Face
Broad lips
Dimples
Thin lips
No dimples
Twin Studies
Monozygotic Twins:
Dizygotic Twins:
•Share 100% same
genes but can have
different
phenotypes
•Genetically no
more similar
than ordinary
siblings
Differences can be
attributed to:
•Share same
fetal
environment
•Don’t always have
same copy of genes
•If develop in
different placentas
(Dizygotic)
(Monozygotic)
Twin Studies & Family Influence
Thomas Bouchard & the Minnesota Twins studies
• If trait genetic:
• closely related more similar than less closely related
• Many close relatives share environments too
• Types of studies to separate effects
•
•
•
•
•
monozygotic twins reared together
monozygotic twins reared apart
siblings/dizygotic reared together
siblings/dizygotic reared apart
adoptive siblings reared together
• Personality characteristics does not seem to be heavily influenced by
environment.
• Environment does impact attitudes, values, manners, faith & politics
• See the famous case of the Jim Twins (watch first 8 min)
Nature or Nurture?
Twin Studies & IQ
Molecular Genetics
• Seeks to identify specific genes that influence behavior
• Hope is to predict the potential of a problem and then take steps to
prevent it.
• Ethical concerns in regards to if this is a good idea?
Heritability
• How much of our differences can be attributed to our differing genes?
• Refers to the variation between the group, NOT the influence of
nature or nurture.
• Heritable trait is one that is capable of being passed down from
parent to child.
• The more similar the environment, the more heritability can explain
differences between people.
Gene-Environment Interaction
• Genes react to the environment.
- Example: nutrition affecting if you’ll reach your genetic potential for height
- See Nature & Nurture: The Study of Twins (4 min) – Prenatal environmental differences
can have long term effects but environment can help one reach their potential.
• Environment acts in response to what genes have given us.
- Example: good looking people are typically treated more kindly by society
• Selection Effects – We select environments that suit our nature.
• Epigenetics – studies how environment can trigger or block genetic expression
• Diet, drugs, stress affect epigenetic molecules on your DNA
• This explains why two identical twins could have the genetic precursor for a mental disorder but only one
ends up having it.