Download Gestation

Psychology of Infancy
Genetics and Prenatal
Development
PSY344W
D. Messinger, Ph.D.
Messinger
Class
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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?
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Who believes in
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Nature – genetics
–
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Nurture – environment
–
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Genes as blueprint
Infinite malleability
Genes and environment working
interdependently and interacting?
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Some basics
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Genes
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Bits of DNA, protein, in each cell
contain information on cell functioning, production,
and reproduction
Chromosomes
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Larger groupings of DNA
All non-gamete cells in the body have 23 pairs of
chromosomes
Half of each pair came from each parent
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Chromosomes
Ordered by karotyping
Reality
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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
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Chromosome 19
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Genomes to Life Project
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Identify the
protein
machines that
carry out
critical life
functions and
the gene
regulatory
networks that
control these
machines
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Terms
 Phenotype
–
Observable trait
 Genotype
–
Genetic pattern associated with the phenotype
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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
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Specific correspondences between genotype
and phenotype
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Blueprint-like
modes of genetic transmission
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Dominant-recessive
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Single gene or Mendellian
 Specific
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–
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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)
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Dominant-Recessive Inheritance
Traits are transmitted as separate units
 Autosomes - 22 pairs
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Non-sex chromosomes
One pair from each parent
When 2 competing traits are inherited
–
Only 1 trait is expressed
 Dominant
trait
 Recessive trait
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Dominant-Recessive Inheritance
Carrier Father (Nr)
+
Carrier Mother (Nr)
Normal
(NN)
Carrier
(Nr)
Carrier
(Nr)
Affected
(rr)
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 aMessinger
carrier as both parents are
Sex-linked inheritance
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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
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Sex-linked inheritance
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Male’s “x” inherited from mother
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Women are carriers
Males represented disproportionately in sex linked
disorders
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baldness color-blindness, hemophilia
–
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Baldness: maternal gf > f
Even sex-linked characteristics are dependent on
environmental influences
–
Expression of baldness depends on circulating
testosterone levels
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Polygenic inheritance – not blueprint like - is the rule
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Multiple genes influence most traits
Sign of polygenic inheritance is range in
phenotype rather than either or
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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
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Disadvantages of the genes-asblueprint metaphor
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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
–
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Without an “environment,” genes are bits of
protein
From a lump of jelly to an organism
–
How do genes actually work?
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Prenatal development is usually
divided into three main periods.
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Zygote –
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Embryo –
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covers the first two weeks after conception
ends when the zygote implants into the wall of the
mother's uterus.
from two to eight weeks following conception
the major organs and bodily systems form
Fetus
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from eight weeks after conception until birth
grows tremendously in size and weight.
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Zygotic cell differentiation
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From zygote to embryo
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The question
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The zygote grows through cell division
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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?
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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
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Gene x Environment interaction
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Environmental factors influence
development from the start
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Cells are environments
The uterus is an environment
The fetus participates in actively
constructing its own development
–
it is not passively constructed
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Creation of a tube
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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
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Stem cell debate
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Brain development
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General pattern of brain development genetically
specified
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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
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Trillions of connections still forming
Trimming of these connections is developmental task
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The fetus as actively constructing
its own development
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Fetal behavior impacts physical
development
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In chicks prevented from moving, cartilage
turns to bone
Fetal sensory experience impacts sensory
development
–
Mice whose tongues were anesthetized had
malformed cleft palates
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Prenatal sensory experience
impacts sensory development
Hearing typically develops before sight
 Rats, ducklings, and quail chicks exposed to
visual stimulation prenatally
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before they normally would
lose hearing ability at birth
 Normal sensory development contingent on
extra-fetal environment
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being enclosed
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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
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2 perspectives on
gene*environment interface
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Transactional
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“It is not nature vs. nurture, but the interaction
of nature and nurture that drives development.”
Urie Bronfrenbrenner (what we just heard)
Quantitative
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The influence of genetic and environmental
factors be distinguished and the influence of
each can be quanitified using behavioral genetic
methods (Plomin)
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Behavioral genetics
Measuring genetic and environmental
influences on behavior
 Finding genes for behaviors?
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Sources of Variance in Behavior
 Genetic
(heritability)
 Environmental
Gene x environment interaction
 Error
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Estimates of genetic and
environmental influence
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Proportional in samples
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Greater environmental variation
 Will
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minimize genetic variation
E.g. Poverty
Greater genetic variation
 Will
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minimize environmental variation
E.g. Downs Syndrome
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Trivia
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Why might adoption studies maximize
estimates of genetic influence?
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Can genetic effects increase with time?
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How?
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Environmental effects
Previously modeled but not measured
 Now parental monitoring, neighborhood
deprivation account for small (2-5%) of
environmental variation
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What else should we be measuring?
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Twin Studies
Monozygotic vs Dizygotic: human studies of
genetic versus environment
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Twin studies
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Identical (MZ) twins share 100% of their
genes
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Fraternal (DZ) twins share 50% of their genes
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genetic duplicates.
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
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Gene * Environment interactions
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Development always involves this interaction
Specific statistical effects
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Genetic effects on alcohol use are great in non-religious
than religious households
Genetic effects on seeking specific environments –
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Identical twins find similar friends
Identical twins treated more similarly (or differently) than
fraternal twins?
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No genetic influence
60
Behavior
Similarity
50
40
30
Twin 1
Twin 2
20
10
0
50% Dizygotic
100% - Monozygotic
Genetic Relatedness
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Complete genetic influence
60
Behavior
Similarity
50
40
30
Twin 1
Twin 2
20
10
0
50% Dizygotic
100% - Monozygotic
Genetic Relatedness
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Additional readings
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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.
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Class
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Syllabus
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