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Chapter 11

PSY100H1 Chapter Notes - Chapter 11: Epigenome, Zygote, Endoderm


Department
Psychology
Course Code
PSY100H1
Professor
Ashley Waggoner Denton
Chapter
11

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11.1 What Does It Mean to Develop
11.1a Nature and Nurture Intertwined
- DNA is turned on or off by the surrounding chemical tags (epigenome) that accumulate through
life
- External environmental factors that can chemically tag our DNA:
- Diet
- nurture
- Stress
- Epigenetic influences accumulare over the life span
- Younger children have more in common than older people because they have
experienced more in life and thus changes their behavior.
11.1b Continuity or Discontinuity
Do traits develop gradually and smoothly over time (continuity) or abruptly from one stage to the next
(discontinuity)
11.1c Universal or Ecological Development
Universal approach:
- Look for age-related behaviors that are found across the entire human species
Ecological approach:
- Ask questions about the impact of culture and environment on development.
11.2 How Do We Change Prenatally?
- First 2 gestational weeks: developing organisms is known as a zygote
- During 2nd gestational week: zygote completes its journey through the mother’s fallopian tube to
the uterus, implanting into the lining.
- Gestational weeks 3 - 8: zygote -> embryo
- Remaining time: Fetus
1st Gestational week:
- Zygote differentiates into 3 germ layers:
1. Ectoderm
a. Develops into nerve tissue and skin
2. Mesoderm
a. Gives rise to muscle and bone
3. Endoderm
a. Source of the body’s soft tissue (organs or digestive tract)
4th Gestational week:
- Central nervous system has been differentiated into:
- Forebrain
- Midbrain

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- Hindbrain
- Spinal cord
7th Gestational week:
- Cells that will form the cerebral cortex begin moving from the lining of the neural tube (which
will develop into ventricles of the brain) to their ultimate destination.
Other systems also begin to differentiate and develop during the embryonic stage.
- Heart, stomach, liver and other organs are formed during this period.
6th gestational week:
- Expression of a gene on the Y chromosome initiates the differentiation of the generic gonads into
testes in males
- While alternate genes guide the development of the gonads into ovaries in males
3rd Gestational month:
- Generic internal reproductive organs differentiate into the uterus, fallopian tubes, and upper
portions of the vagina in females
- Generic internal reproductive organs differentiate into the seminal vesicles, vas deferens, and
prostate in males.
- New neurons are born in large numbers and begin forming connections with each other
6th Gestational month:
- Myelination of the nervous system
- Allows neurons to communicate faster and more efficiently
7th Gestational month:
- Most of the brain’s cells have been formed
The fetus is able to hear noises outside the mother’s body during the last few months of pregnancy and
thus newborn babies show an immediate preference for their mother’s voice.
- Advantages in the attachment and bonding that occurs between mother and newborn.
Most pregnancies last about 40 weeks
- Babies are born between gestational week 37 and 42.
- Premature infants are at greater risk than term infants because of the development of the organs,
etc.
11.2a Genetic Risks to Development
The more common genetic abnormalities seen in children are those that become more likely when their
parents are older.
- Errors in the development of eggs and sperm in older parents
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Pregnancies in Older Parents:
Because the final division of a woman’s immature egg (formed during prenatal stage) into a mature ovum
does not occur until before ovulation:
- A 40-year-old woman’s eggs have been exposed to 40 years of potentially harmful environmental
influences that raises the probability that something will go wrong as they divide.
- Thus there may be errors in the development of eggs
- There aren’t many defects that can occur with sperm because a man takes a little over 2 months to
produce sperm cells thus reducing their chances of exposure to harmful influences.
Down syndrome / trisomy 21:
- Results when child receives a third full / partial copy of the 21st chromosome along with the
usual 2 due to faulty cell division.
- Results in intellectual disability, a pattern of mild physical abnormalities
- Lifespan of only 40-50 years.
- A woman’s chances of giving birth to a child with DS are:
- Age 20: 1/2000
- Age 45: 1/30
11.2b Environmental Risks to Development
During pregnancy:
- Developing fetus is protected from exposure to toxins and disease-causing agents by the placenta
(organ attached to the wall of the mother’s uterus that provides the fetus with nutrients and
oxygen)
- Relatively safe because substances that are safe for the mother can have devastating
effects on the health and development of her fetus.
Teratogen:
- Any agent that can produce harmful effects in the zygote, embryo, or fetus
- Example:
- exposure to commonly used antidepressant medications -> higher rates of
premature birth and ASD.
- Use of acetaminophen (tylenol and anacin) during pregnancy -> higher risk for
ADHD in children
- Use of antifungal medications by pregnant woman -> reduces masculinization of
her male offspring
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