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Behavior Genetics


									Behavior Genetics
Chromosomes, Genes, & You
• 23 pairs of rod-like structures within nuclei
  of cells
• Genes, composed of DNA
• DNA is template for production of RNA
• RNA produces proteins from amino acids
• You are a collection of proteins
Human Chromosomes
     Genes and Environment
• Need both genes and environment for life
• Different environments  different
• Different genes  different developments
• Gene x Environment Interaction
  – effect of gene depends on type of
  – effect of environment depends on genes
        Mitosis and Meiosis
• Mitosis – exact duplication of DNA
• Meiosis – production of eggs and sperm
• Crossing Over – exchange of material
  between paired chromosomes
• Each gamete gets only one chromosome
  from each pair
• Random Assortment of chromosomes
• No two gametes likely identical
       Sexual Reproduction
• Produces genetic diversity in offspring
• Good strategy for dealing with a changing
• In steady environment asexual
  reproduction is better strategy.
• Hydras change back and forth between
  sexual and asexual
• Some species lost the ability to reproduce
Hydra in Pond Water
             Defining Sex
• Female = makes few but large gametes
• Male = makes many but small gametes
• Chromosomal sex:
  – Humans: XX = female, XY = male
  – Birds: ZZ = male, ZW = female
  – Some Insects: XX = female, X0 = male
• Hormonal sex
• Genital sex
• Gender identity
          Simple Inheritance
• Locus -- location of gene on chromosome
• Alleles -- different forms of genes that can
  be found at a locus.
• Homozygous -- same allele on both
• Heterozygous -- different alleles
• Phenotype – observable characteristics
• Genotype – genetic composition
           A/B/O Blood Types
•   The A gene codes for protein A
•   The B gene codes for protein B
•   The O gene codes for no protein
•   A and B are dominant over O.
•   AA or AO – blood type A
•   BB or BO – blood type B
•   AB – both proteins produced (codominance)
•   OO – blood type O
           Genetic Context
• Action of a gene depends on other genes
• May be dominant in one genetic context,
  recessive in another.
• Gene as a funnel in a series.
• The smallest funnel limits the rate of flow
  and determines the outcome.
Rate Limiting Step
      Red/White Snapdragons
• The red/white gene controls a rate-limiting step.
• Homozygous white – very little of the enzyme
  associated with red coloration is present.
• Heterozygous – medium amount of enzyme,
  pink flowers.
• Homozygous Red – lots of the enzyme, red
• Codominance – both genes affect flower color.
    Purple/White Pea Flowers
• Is a threshold amount of chemical necessary to
  make flowers purple.
• At rate limiting step one allele allows for
  production of not enough for purple.
• Other allele (dominant) allows for enough to
  make flowers purple.
• If have one or two of the dominant genes,
  flowers are purple.
• Dominance – the recessive genes have an effect
  only in the homozygous condition.
The Basenji is fearful of strangers.
The cocker spaniel is not.
What About A Cockenji?
      Inheritance of Fearfulness
•   John Paul Scott and John Fuller
•   Basenji x Basenji  fearful pups
•   Cocker x Cocker  fearless pups
•   Basenji x Cocker  fearful pups
•   Dominant F gene codes for Fearfulness
•   Recessive f gene codes for fearlessness
•   F1 dogs are heterozygous, Ff
Breed F1 Dogs With Each Other

Father       F             f
   F        FF         Ff
    f        fF            ff
Backcross F1 Dogs With Cockers

Cocker        F          f
   f         fF          ff
   f         fF          ff
Backcross F1 Dogs With Basenji

Basenji       F         f
   F         FF         Ff
   F         FF         Ff
  Nature & Nurture: Heritability
• Nature = Effect of genes
• Nurture = Effect of environment/learning
• What % of differences among individuals
  in a population are due to genetic
  differences among the individuals.
• Inbred mice: 0%
• Outbred mice in controlled environment:
       Behaviorists’ Delusion
• If a trait can be modified by environmental
  change or learning, it must have been
  established by environmental factors.
• PKU – genetically caused inability to
  metabolize properly certain foods.
• Detected by testing babies’ blood.
• Treated environmentally – avoid certain
         Habitat Selection
• Genes  Habitat Selection  Behavioral
• Two subspecies of Peromyscus
• One normally lives in the forest.
• The other in the prairie.
• What causes behavioral differences
  between the subspecies, genes or
The Deer Mouse
Wecker, 1964, Scientific American
• Gave field-caught mice choice of habitat.
• They chose the one typical of their
• Gave lab-born mice choice of habitat.
• Ditto. Their genes determined their choice
• If the habitat affects a behavioral trait, is
  that due to environment (proximal) or
  genes (ultimately)?
   Parenting Styles and Offspring
• Observed correlation between parenting
  style and competence of child.
• Parental style  child’s competence ?
• Different babies evoke different parental
• Child’s genes  child’s competence 
  parental style ?
• Child’s genes  child’s behavior 
  parental style  child’s competence ?
       Inheritance of Polygenic
• Tryon, 1940 – Maze intelligence of rats.
• Breed brightest with brightest, dullest with
• Six generations – two new strains of rats.
• Cross-Fostering to control for effect of
  parental style.
  Cross-Fostering and Maze
         Biological Mother
Foster    Bright      Dull
Bright      25         15
 Dull       20         10
      Inheritance in Humans
• Can’t do selective breeding experiments
• Can correlate genetic similarity with
  psychological similarity
• Of those genes on which humans differ,
  what percentage do you share with your
  – monozygotic twin – 100%
  – dizygotic twin, sibling, parent – 50%
  – half-sib, grandparent, aunt, uncle – 25%
  – cousin, great grandparent – 12.5%
         Monozygotic Twins
• Obtain many pairs of
  monozygotic twins.
• Measure each twin on
                          Pair a b c d e f
  some characteristic,
  such as intelligence.   one 1 3 6 7 8 9
• Compute Pearson r.      other 3 4 4 5 8 7
• Here r = .85
           Nontwin Siblings
• Obtain many pairs of
  nontwin siblings.
• Measure each sib.      Pair a b c d e f
• Compute Pearson r      one 1 3 6 7 8 9
• Here r = .47           other 5 1 4 9 5 6
• Do same with aunts,
  cousins, etc.
• r decreases as does
  genetic similarity
     Genetic and Psychological
• Data like these can be use to estimate
• Extroversion
• Neuroticism
• Dominance and aggressiveness
• Intelligence
• Even political conservativism.
   If Your Mother Took Home the
            Wrong Baby
• Would that baby have grown up to be just
  like you are now? (Do genes matter?)
• Would you, raised by other parents, have
  turned out the same? (Does environment
   Reluctance to Accept Behavior
• Accept that genes affect physical
  characteristics, but
• Resist idea that they affect mental and
  behavioral characteristics.
• The delusion of free will.
• We did not chose our genes.
• If they determine our behavior, our will is
  not free.
   Genes  Nervous System
• The brain and nervous system is a
  physical characteristic.
• Genes affect its development.
• Our mental states and behavior are under
  the control of the brain and nervous
• Thus, genes affect our mental life and
    If Your Mom Took a Puppy Home
            From the Hospital
• Instead of you
• And raised it as her child.
• Would that dog be just like you are now?
• Of course not.
• Genes explain differences between
• Why not differences between individuals of
  same species?
• All persons should have equal political and
  social rights.
• Do all have to be equal to have equal
• If so, behavior genetics is a threat to
• I think not. We should celebrate our
  diversity, not deny it.
 Racism and Behavior Genetics
• Immigration policy, IQ, and national origin
• Other racist BS (Bad Science)
• No good evidence that genes related to
  skin color are directly related to
  psychological attributes.
      Correlates of Skin Color
• Skin color can be indirectly related to
  psychological attributes in a racist society.
• Imagine Blue People subject to racial
• Not given same economic & social rights.
• Such racism would cause Blue People to
  differ psychologically from others.
The Blue Fugates
            Blue Hemoglobin
•   Methemoglobin
•   Diaphorase normally converts to red.
•   Recessive condition = no diaphorase
•   Inbreeding in remote locations
•   Treatment with methylene blue.
            Martin Fugate
• A blue Frenchman.
• 1820, Troublesome Creek, Eastern KY.
• Wife carried the recessive gene.
• Four of their seven children were blue.
• The blue clan spread in isolated
• Later, coal mining and railroads brought
  new people, outbreeding.
            Benjamin Stacy
• Very blue at birth, rushed to hospital in
• Discovered he descended from Martin
• Is now relatively normal in color.
• Lips and nails turn blue when cold or
          Genetic Engineering
•   1985, Monsanto Company
•   Human gene transferred in petunia plants
•   Human chorionic gonadotropin.
•   Medically used to induce ovulation
•   & to stimulate production of testosterone.
•   Gene was passed on to next generation of
              Firefly Tobacco
•   1986, UC San Diego
•   Gene from firefly transferred to tobacco.
•   Produce enzyme luciferase.
•   Plant glows in the dark.
•   Also transferred to monkey cells.
         Firefly Tuberculosis
• 1993, Albert Einstein College of Medicine.
• Firefly genes into TB bacteria.
• If healthy, the bacteria glow.
• If an antibiotic weakens them, stop
• Allows more rapid identification of effective
  antibiotic for new strains of TB.
Jellyfish Glow Pigs
               Genetic Testing
•   Do you have genes that lead to disease?
•   Identify them, treat the disease now.
•   Don’t let your employer know.
•   Don’t let your insurer know.
•   California HMO
    – Fetus has gene for cystic fibrosis
    – Will pay for abortion
    – Will not pay to care for child if born.
Check Chromosomes in Sperm
•   Infertility maybe due to bad sperms?
•   Check the sperms’ chromosomes.
•   Can’t do it until has fertilized an egg.
•   Ethical problems using a human egg.
•   Practical problems using a human egg.
•   So use a hamster egg.
•   Ryuzo Yanagimachi, 1970’s, Univ. Hawaii
From Ryuzo’s Lab
 Jellyfish Glow Mice

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