Psychology of Infancy

Genetics and Prenatal Development

PSY344W D. Messinger, Ph.D.

Messinger

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?

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Who believes in  Nature – genetics – Genes as blueprint  Nurture – environment – Infinite malleability  Genes and environment working interdependently and interacting? Messinger

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 Messinger

Chromosomes Reality Ordered by karotyping Messinger

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 Messinger

Chromosome 19 Messinger

Genomes to Life Project  Identify the protein machines that carry out critical life functions and the gene regulatory networks that control these machines Messinger

Terms  Phenotype – Observable trait  Genotype – Genetic pattern associated with the phenotype Messinger

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 Messinger

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) Messinger

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 Messinger

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 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 Messinger

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 Messinger

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 Messinger

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?

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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. Messinger

Zygotic cell differentiation Messinger

From zygote to embryo Messinger

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?

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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 Messinger

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 Messinger

Creation of a tube Messinger

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 Messinger

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 Messinger

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 Messinger

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 Messinger

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 Messinger

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) Messinger

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 Messinger

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 Messinger

Trivia  Why might adoption studies maximize estimates of genetic influence?

 Can genetic effects increase with time?

– 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 – What else should we be measuring?

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Twin Studies Monozygotic vs Dizygotic: human studies of genetic versus environment Messinger

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

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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?

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No genetic influence

60 50 40 30 20 10 0 50% Dizygotic 100% - Monozygotic Genetic Relatedness

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Twin 1 Twin 2

Complete genetic influence

60 50 40 30 20 10 0 50% Dizygotic 100% - Monozygotic Genetic Relatedness Twin 1 Twin 2

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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.

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Class  Syllabus Messinger