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Messinger Genetics and Prenatal Development

Messinger Genetics and Prenatal Development






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Messinger Genetics and Prenatal Development Messinger Genetics and Prenatal Development Presentation Transcript

  • Genetics and Prenatal Development PSY344W D. Messinger, Ph.D. Psychology of Infancy
  • Class
    • What are the advantages (name some forms of genetic transmission) and disadvantages of thinking of genes as blueprints?
    • How do environmental and genetic influences interact during prenatal development (provide examples)?
    • What is the difference between transactional and a behavioral genetics approach to gene * environment interactions?
  • Who believes in
    • Nature – genetics
      • Genes as blueprint
    • Nurture – environment
      • Infinite malleability
    • Genes and environment working interdependently and interacting?
  • Some basics
    • Genes
      • Bits of DNA, protein, in each cell
      • contain information on cell functioning, production, and reproduction
    • Chromosomes
      • Larger groupings of DNA
      • All non-gamete cells in the body have 23 pairs of chromosomes
      • Half of each pair came from each parent
  • Chromosomes Reality Ordered by karotyping
  • Human genome project
    • identify all the approximately 30,000 genes in human DNA,
    • determine the sequences of the 3 billion chemical base pairs that make up human DNA,
    • 99.9% (of nucleotide bases) are the same in all people
  • Chromosome 19
  • Genomes to Life Project
    • Identify the protein machines that carry out critical life functions and the gene regulatory networks that control these machines
  • Terms
    • Phenotype
      • Observable trait
    • Genotype
      • Genetic pattern associated with the phenotype
  • How are genes a blueprint?
    • “The DNA sequence (e.g., ATTCCGGA) . . . spells out the exact instructions required to create a particular organism with its own unique traits.”
    • A metaphor which describes some aspects of phenomenon
      • Specific correspondences between genotype and phenotype
  • Blueprint-like modes of genetic transmission
    • Dominant-recessive
      • Single gene or Mendellian
        • Specific genetic defects can be deadly or disabling
        • http://www.uaf.edu/psych/psyc240/exam1/index.html, Jim Allen , Ph.D
      • Phenylkitenuria, sickle cell, etc.
    • Sex-linked (23rd chromosome)
  • Dominant-Recessive Inheritance
    • Traits are transmitted as separate units
    • Autosomes - 22 pairs
      • Non-sex chromosomes
      • One pair from each parent
    • When 2 competing traits are inherited
      • Only 1 trait is expressed
        • Dominant trait
        • Recessive trait
  • Dominant-Recessive Inheritance
    • Traits are transmitted as separate units
      • 25% risk of inheriting a “double-dose” of r genes
        • which may cause a serious birth defect
      • 25% chance of inheriting two N ’s
        • thus being unaffected
      • 50% chance of being a carrier as both parents are
  • Sex-linked inheritance
    • 23rd chromosomal pair
    • Female = XX
      • each branch is matched
    • Male = XY (Missing an arm)
      • one Y branch not matched
      • so allele on corresponding X branch is expressed
  • Sex-linked inheritance
    • Male’s “x” inherited from mother
      • Women are carriers
      • Males represented disproportionately in sex linked disorders
        • baldness color-blindness, hemophilia
          • Baldness: maternal gf > f
    • Even sex-linked characteristics are dependent on environmental influences
      • Expression of baldness depends on circulating testosterone levels
  • Polygenic inheritance – not blue-print like - is the rule
    • Multiple genes influence most traits
    • Sign of polygenic inheritance is range in phenotype rather than either or
      • skin/eye/hair color, height, baldness, personality
      • Reaction Range
      • Potential variability in expression of a trait
    • Such traits may also be susceptible to environmental influence
  • Putting genes in their environment
    • Meiosis
      • Each pair splits
      • Producing gamete with unique set of chromosomes
    • Gametes - sex cells
      • Sperm
      • Ovum
    • Fertilization of the ovum creates the zygote - New Cell
  • Disadvantages of the genes-as-blueprint metaphor
    • Genes are bits of protein in a primarily liquid nucleus in a primarily liquid cell surrounded by other cells in a primarily liquid uterine environment
      • Without an “environment,” genes are bits of protein
    • From a lump of jelly to an organism
      • How do genes actually work?
  • Prenatal development is usually divided into three main periods.
    • Zygote -
      • covers the first two weeks after conception
      • ends when the zygote implants into the wall of the mother's uterus.
    • Embryo -
      • from two to eight weeks following conception
      • the major organs and bodily systems form
    • Fetus
      • from eight weeks after conception until birth
      • grows tremendously in size and weight.
  • Zygotic cell differentiation
  • From zygote to embryo
  • The question
    • The zygote grows through cell division
      • Mitosis - One for one copying of all 23 chromosomes
    • All cells contain the same genetic information in their nuclei
    • But qualitatively different types of cells develop in different parts of the body
    • How does this occur?
  • General processes yield specific outcomes
    • Cells clump together as a sphere
    • This changes the extra-cellular environment of cells on the inside and outside of the sphere
    • Differences in environment impact cell’s genetic make-up to activate different proteins
  • Gene x Environment interaction
    • Environmental factors influence development from the start
      • Cells are environments
      • The uterus is an environment
    • The fetus participates in actively constructing its own development
      • it is not passively constructed
  • Creation of a tube
  • Embryology
    • Cells groups in which specific molecular processes occur with boundaries with other groups
    • Regulator genes activate and de-activate other genes within these groups
    • Cells impact each other such that a nerve cell transplanted to the liver region becomes a liver cell after several replications
      • Stem cell debate
  • Period of the fetus
    • from eight weeks after conception until birth
    • grows tremendously in size and weight.
    • recognizable human shape
    • though it still weighs less than an ounce.
  • Brain development
    • General pattern of brain development genetically specified
      • By 20 weeks, most neurons present
      • 3rd - 16th prenatal week most crucial
      • At 8 weeks, head is half of fetus
    • But specific connections depend on generic growth processes and sensory-motor stimulation
      • Trillions of connections still forming
      • Trimming of these connections is developmental task
  • The fetus as actively constructing its own development
    • Fetal behavior impacts physical development
      • In chicks prevented from moving, cartilage turns to bone
    • Fetal sensory experience impacts sensory development
      • Mice whose tongues were anesthetized had malformed cleft palates
  • Prenatal sensory experience impacts sensory development
    • Hearing typically develops before sight
    • Rats, ducklings, and quail chicks exposed to visual stimulation prenatally
      • before they normally would
    • lose hearing ability at birth
    • Normal sensory development contingent on extra-fetal environment
      • being enclosed
  • Prenatal behavioral development
    • 9 weeks - movement
    • 16 weeks - frowning, grimacing
    • 25 weeks - moves to drumbeat
    • 26 weeks - remembers sounds
    • 32 weeks - all brain areas functioning
    • 34 weeks - can habituate
  • 2 perspectives on gene*environment interface
    • Transactional
      • “ It is not nature vs. nurture, but the interaction of nature and nurture that drives development.” Urie Bronfrenbrenner (what we just heard)
    • Quantitative
      • The influence of genetic and environmental factors be distinguished and the influence of each can be quanitified using behavioral genetic methods (Plomin)
  • Behavioral genetics
    • Measuring genetic and environmental influences on behavior
    • Finding genes for behaviors?
  • Sources of Variance in Behavior
    • Genetic (heritability)
    • Environmental
    • Gene x environment interaction
    • Error
  • Estimates of genetic and environmental influence
    • Proportional in samples
      • Greater environmental variation
        • Will minimize genetic variation
          • E.g. Poverty
      • Greater genetic variation
        • Will minimize environmental variation
          • E.g. Downs Syndrome
  • Trivia
    • Why might adoption studies maximize estimates of genetic influence?
    • Can genetic effects increase with time?
      • How?
  • Environmental effects
    • Previously modeled but not measured
    • Now parental monitoring, neighborhood deprivation account for small (2-5%) of environmental variation
      • What else should we be measuring?
  • Twin Studies Monozygotic vs Dizygotic: human studies of genetic versus environment
  • Twin studies
    • Identical (MZ) twins share 100% of their genes
      • genetic duplicates.
    • Fraternal (DZ) twins share 50% of their genes
      • on average
    • Both types of twins have similar environments . . .
    • Greater behavioral similarity of identical twins indexes greater genetic influence
            • http://www.psych.umn.edu/psylabs/mtfs/special.htm
  • Gene * Environment interactions
    • Development always involves this interaction
    • Specific statistical effects
      • Genetic effects on alcohol use are great in non-religious than religious households
      • Genetic effects on seeking specific environments –
        • Identical twins find similar friends
        • Identical twins treated more similarly (or differently) than fraternal twins?
  • No genetic influence
  • Complete genetic influence
  • Additional readings
    • Plomin, et al. The genetic basis of complex human behaviors.
    • Plomin, R., & Rutter, M. (1998). Child development, molecular genetics, and what to do with genes once they are found. Child Development, 69 (4), 1223-1242.
    • Rutter. M. (in press [2002]. Nature, nurture, and development: From evangelism through science towards policy and practice. Child Development .
    • Collins , W. A., Maccoby, E. E., Steinberg, L., Hetherington, E. M., & Bornstein, M. H. (2000). Contemporary research on parenting: The case for nature and nurture. American Psychologist, 55(2), 218-232.
    • Sleigh, M. J., Columbus, R. F., & Lickliter, R. (1998). Intersensory experience and early perceptual development: Postnatal experience with multimodal maternal cues affects intersensory responsiveness in Bobwhite Quail Chicks. Developmental Psychology, 34 (2), 215-223.
  • Class
    • Syllabus