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The Start of Life: Prenatal Development
Chapter 2
Robert S. Feldman

EARLIEST DEVELOPMENT
Beginning of Life
Gametes from male and female join
Ovum and sperm
Fused gametes create zygote
Period of the Zygote
The Code of Life
Genes
DNA
Chromosomes
Rod-shaped DNA portions in 23 pairs
Contain genetic blueprint for individuals
Replicate through mitosis



And baby makes two or three or more!
Multiple births
Monozygotic
Dizygotic



What causes multiple births?
Fertility drugs
Older mothers
Racial, ethnic, and national differences
Mixing and Matching of Genes
Basics of genetics
DOMINANT TRAITS
RECESSIVE TRAITS

Just the right type
GENOTYPE – underlying combination of genetic material
Homozygous (similar forms of gene from parents)
Heterozygous (different forms of gene from parents)
PHENOTYPE – observable trait
X-Linked recessive genes
Genetic Information Transmission
Let’s turn to Figure 2-4 in the text to examine PKU probabilities
Genetic Inheritance
Most traits are NOT dominant-recessive.

Most traits are polygenic and vary in terms of reaction range.
Cracking the Genetic Code
The Human Genome
National Human Genome Research Institute
(http://www.genome.gov/)




In what ways can information from the Human Genome Project affect your life?
When Development Deviates
Causes
Genetics
Spontaneous mutation
Environmental insult

Behavioral Genetics
When Development Deviates
Consequences
Down Syndrome
Fragile X Syndrome
Sickle-cell Anemia
Tay-Sachs Disease
Klinefelter’s Syndrome



Genetic Counseling
Can you name three diseases for which DNA-based genetic tests are available?
(Hint: see Table 2-3)
Prenatal Testing
Amniocentesis
CVS embryoscopy
FBS
Sonoembryology
Sonogram
Ultrasound sonography

Should pre-implantation sorting be available to all families?
THE INTERACTION OF HEREDITY AND ENVIRONMENT
Studying Development
Nonhuman animal studies
Controlling genetics and environment

Human studies
Adoption
Twin studies
Family studies
Do you have your mother’s eyes?
Family resemblances
More genetically similaritymore likely to share physical characteristics
What do you think?
A given behavior is not caused just by genetic factors, nor is it caused solely by environmental factors.

MULTIFACTORIAL TRANSMISSION: many traits determined by combination of both genetic & environmental factors
Genotype provides range of expression
Environment determines expression as phenotype
Nature, Nurture, and Intelligence
Relative contributions of nature and nurture highly researched
Closer genetic link = greater correspondence of overall IQ scores



Genetics and I.Q.
Range of Possibilities
Determinants of Intelligence





Do we inherit our personality?
A link look
Two of “Big Five” personality traits linked to genetic factors:
Neuroticism
Extroversion

What evidence supports this claim?
What about environmental influences?
Culture
Parental encouragement
Developmental Diversity
Can a culture’s philosophical outlook be determined by genetics?
Kagan and colleagues
What about mental illness?
Many mental illnesses and disorders have a genetic component as well.

Schizophrenia
Depression
Autism
ADHD

Fundamental Principle
Within debate about relative influence of nature and nurture
Role of genetics is often to produce tendency toward future course of development
Role of environment affects when and whether a certain behavioral characteristic will actually be displayed
Gene-environmental Influence
Sandra Scarr suggests three ways child’s genetic predisposition may influence his or her environment:
Passive
Evocative
Active


Three Types of Interaction
Passive genotype-environment interaction (parent’s genotype influences type of environment where kids are raised)
Ex. of positive passive interaction: parents & child naturally sociable, parents provide social activity; athletic parents provide sports opportunities to athletic child
Ex. of negative passive interaction: sociable parents and introverted child, child uncomfortable in environment; athletic parents pressure
Three Types of Interaction
2. Evocative genotype-environment interaction (child's genotype affects how others react to him/her, elicit a type of environment).

Ex. of positive: smiling, sociable baby gets more social stimulation and reinforcement

Ex. of negative: strong-willed, difficult child gets negative attention
Three Types of Interaction
3. Active genotype-environment interaction (children focus on or seek out aspects of the environment that are congruent with their genetic abilities).

Also known as “niche-picking,” for example, seeking out involvement in sports or music
PRENATAL GROWTH AND CHANGE
Fertilization
Moment of conception
Joining of sperm and ovum = zygote




Stages of Prenatal Development
Germinal
Embryonic
Fetal
(See Table 2-5 for a concise review)
Germinal Stage
Fertilization  two weeks
Shortest stage
Fertilized egg now called blastocyst
Travels to and implants in uterus
Characterized by methodical cell division
32 cells by day 3, 100-150 within first week
With division comes cell specialization
Embryonic Stage
2 weeks  8 weeks
Organism firmly secures to uterus and called an embryo
Development of major organs and basic anatomy
Three distinct layers that ultimately form different set of structures:
Ectoderm
Endoderm
Mesoderm
Embryonic Stage
At end of embryonic stage:
1 inch long, gills and tail-like structure; rudimentary eyes, lips, teeth, stubby bulges that become arms and legs
Head grows rapidly and begins to represent significant portion of body (50% of total length)
Rapid growth of nerve cells (100,000 neurons produced EVERY MINUTE)
Nervous system begins to function at 3 weeks and at 5 weeks weak brain waves detected

Embryonic Stage
Every part of body formed with these layers

Fetal Stage
8 weeks  Birth
Formally starts when differentiation of major organs has occurred
Organism now called fetus
Characterized by rapid development
Organs become more differentiated and begin working
Interconnections between body parents become more complex and integrated
Brain becomes more sophisticated
Pregnancy Problems
Infertility
Miscarriage
Abortion
Pregnancy Problems
Infertility: 15% of couples; inability to conceive after 12 to 18 months
Maternal infertility influenced by age; hormone imbalance, damaged fallopian tubes or uterus, stress, abuse of alcohol or drugs
Paternal infertility influenced by illicit drugs, tobacco, STDs
Artificial insemination; IVF; GIFT; ZIFT; ethical issues
Pregnancy Problems
Miscarriage: spontaneous abortion
15-20% pregnancies end in miscarriages
many times genetic abnormality

Abortion: voluntary termination pregnancy
Aftereffects
may contribute to increase in future pregnancies
Threats to Development
Prenatal environment
Teratogen
(See Figure 2-15 for a teratogen sensitivity timeline)
Teratogen Sensitivity Timeline
Mother’s Prenatal Influence
Mother’s
Diet
Age (too young or too old)
Prenatal support
Health
Drug use
Alcohol use
Tobacco use

Father’s Prenatal Influence
Relatively little research
Tobacco use (secondhand smoke)
Drug use
Alcohol use
Treatment of mother
Becoming an Informed Consumer Optimizing the Prenatal Environment