CHAPTER 2:
GENETIC BASES
OF CHILD DEVELOPMENT
JANUARY 16, 2023
The Genetic Code
• genotype = an individual’s complete
set of inherited traits
• phenotype = directly observable
characteristics
Principles of Genetics
• For single-gene traits, phenotype
expressed through combinations of
dominant and recessive alleles
• Allele = one variant of the gene
Principles of Genetics
• Homozygous
– Both alleles are the
same (BB or bb)
• Heterozygous
– Alleles are different (Bb)
• Dominant trait
– Shows up in both cases
• Recessive trait
– Show up when alleles
are homozygous only
Principles of Genetics
• Note: most traits are multiply
determined (polygenic)
• E.g., intelligence, personality
Heritability
• Def: an estimate of the proportion of
trait variability in a population that is
determined by genetic differences
• E.g., heritability of height = 90%
• Note: Accounts for differences within
groups, not within individuals
Ways of Determining Heritability
• 1. Twin studies
• 2. Adoption studies
Twins
• Monozygotic (identical):
• union of one egg and one sperm
that splits in two, soon after
conception
• Genetic relatedness: 100%
• Dizygotic (fraternal):
• two different eggs fertilized by two
different sperm
• Genetic relatedness: 50%
Relationship
Shared
Home?
% Shared
Genes
Correlation btw.
Intelligence
scores (r)
Identical twins
Yes
100%
.86
Identical twins
No
100%
.78
Fraternal twins
Yes
50%
.60
Relationship
Shared
Home?
% Shared
Genes
Correlation btw.
Intelligence
scores (r)
Identical twins
Yes
100%
.86
Identical twins
No
100%
.78
Fraternal twins
Yes
50%
.60
Parent &
biological
child
Yes
50%
.42
Parent &
biological
child
No
50%
.24
Non-bio.
parent &
adopted child
Yes
0%
.19
Turkheimer et al., 2003
Heritability
of IQ scores
Genotypes, Phenotypes, and Human Behavior
• Niche Construction:
– Refers to how behaviors, activities, and
choices of individuals actively shape and
modify the environment in which they live
• E.g.: athletic build: involvement in sports
CHAPTER 3:
PRENATAL DEVELOPMENT
AND BIRTH
January 16, 2023
B. Pregnancy: Fact vs. Fiction
Pregnancy: Fact vs. Fiction
• #1. You can tell your baby's sex by the way
you are carrying, or by the fetal heartbeat.
»MYTH
• Ultrasound and amniocentesis are the only
ways you can tell
Pregnancy: Fact vs. Fiction
• #2. Having sex during pregnancy can
hurt the baby.
• MYTH
• Only if it’s a high-risk pregnancy;
otherwise harmless
Pregnancy: Fact vs. Fiction
• #3: Pregnant women only feel sick in
the morning.
»MYTH
• Nausea can happen any time of day,
depending on hormone fluctuation
I. THE PERIOD OF PRENATAL
DEVELOPMENT
1. Germinal Period
• From conception until zygote
enters uterus and becomes
implanted (8 to 10 days after
conception)
• Organism has grown from a single
cell to hundreds of cells
1. Germinal Period
• Placenta forms –
allows food & oxygen
to reach zygote
• Connected via
umbilical cord
2. Embryonic Period
• From implantation until end of 8th week
• All major organs have taken primitive shape
• Sexual differentiation has begun
3. Fetal Period
• 9th week until birth
• The fetus dramatically grows in
weight and length.
• The brain and all organ systems
increase in complexity.
• Age of viability: 22-26 weeks
3. Fetal Period
• Basic sensory capacities developing
– E.g.: sensing motion, light, sound
• Environmental influences from outside and
inside the mother can affect fetal
development.
– E.g.: mother’s diet and illnesses
II. Maternal Conditions and
Prenatal Development
Teratogens
• Teratogens: agents that cause
damage to an embryo or fetus
• Greatest risk during first 8 weeks of
gestation
Teratogens
•
•
•
•
Categories:
a) diseases
b) drugs
c) environmental hazards
Other General Risk Factors
• 1. Nutrition
– Inadequate maternal nutrition may
result in premature birth and low birth
weight
– Lack of folic acid may increase risk of
spina bifida
Other General Risk Factors
• 2. Stress
– Studies show extreme maternal stress is
associated with low birth weight and
premature births
– Can also reduce child’s phys. capacity
to manage stress
Other General Risk Factors
• 3. Mother’s Age
– Older mothers are more likely to have
difficulty getting pregnant, miscarriages,
and stillbirths
– Nearly 50% of pregnancies among
women in their 40s / 50s result in
miscarriage
III. BIRTH
The Stages of Labour
– Normally begins approx. 266 days
after conception
– Proceeds through three stages
1. Dilation of cervix
2. Delivery of baby
3. “Birth” of placenta
Would you like fries with that?
Birth: Cultural Variations
• Childbirth practices influenced by
culture
• E.g., Bajura, Nepal
• Expectant mothers isolated, deliver
own babies
• E.g. Pokot people of Kenya
• Community celebration
Birth: Cultural Variations
• North America
• Childbirth Experiences:
– 1. Be assisted by physician or midwife at
hospital (more common)
– 2. Be assisted by midwife and/or others at
home (increasing in popularity)
Approaches to Birth
1. Natural childbirth
- Techniques aimed at reducing pain
and medical intervention; make
childbirth a rewarding experience
- Mothers often give birth in upright,
sitting position
Approaches to Birth
• 2. Home Delivery
• Safe for healthy women accompanied
by trained midwife or doctor
Approaches to Birth
• 3. Labour & Delivery Medication
• Used in 80% of N. American births
• E.g., epidural analgesia
– Can weaken uterine contractions
– Affects baby, temporarily
The Baby’s Experience of Birth
• A stressful experience
• Surge of stress hormones
– Necessary for lungs to function properly
– Increase metabolic rate
– Induces state of alertness
IV: THE NEWBORN
Physical Condition
• The Apgar Scale (0-10)
– Assesses physical condition
– Factors rated:
– Heart rate
– Respiratory effort
– Muscle tone
– Reflex responsivity
– Color
– A low score requires immediate
medical attention
Behavioral Condition
• Brazelton Neonatal
Assessment Scale
– Assesses subtle behavioral
aspects of newborn’s condition
– Includes tests of:
– Reflexes
– Motor capacities
– Responsiveness to objects
and people
Problems and Complications
• Prematurity
– Birth > 3 weeks before due
date
– Immature lungs, digestive,
or immune systems
• Low Birth Weight
– Below 5 pounds, 8 ounces
(2500 grams)
– At greater risk for
complications
Problems and Complications
• Main causes for low birth weight:
poor nutrition, heavy drug / alcohol
use, multiple births
Consequences of Low Birth Weight
• Breathing difficulties
– E.g., Respiratory distress syndrome
• Often spend time in isolette
Consequences of Low Birth Weight
• Special infant stimulation (kangaroo
care) provides benefits
Newborn Reflexes
• Reflexes
– Involuntary
– Some have important functions (e.g.,
sucking reflex)
– Some serve as building blocks for later
actions (e.g., stepping reflex as
precursor to walking)
Newborn States
•
•
•
•
Alert inactivity
Waking activity
Crying
Sleeping
Infants’ Sleep
• 16-18 hrs/day
– Alternates from being
still and breathing
regularly (non-REM) to
moving gently and
breathing irregularly
(REM)
– Awake one hour / sleep
3 hours
Infants’ Sleep
• By 1 month: 15 hrs / day
• By 4 months: 14 hrs / day
• Coincide more with typical adult
schedule
Sudden Unexpected Infant Death (SUID)
• The sudden, unexplainable death of an
apparently healthy baby
• Rate in Canada is decreasing, but higher for
Indigenous than non-Indigenous populations
• Risk factors:
– child sleeping on stomach (esp. when
other items in crib)
– parents’ smoking
– maternal malnutrition
Sleeping Arrangements
• Individualist cultures: favour separate
crib for infant
• Collectivist cultures: favour cosleeping
Crying
• Means of communication – evolved mechanism?
• Varies in intensity
• Several possible interpretations… parents’
accuracy improves with experience
Soothing a Crying Infant
•
•
•
•
•
Feeding
Changing diaper
Picking up
Rocking / bouncing
Swaddling
Don’t Shake The Baby!!!
• Shaken baby syndrome
• Results in severe head trauma or
death