Chapter 4 - 6

Chapter 4

Nature vs. Nurture

  • Nature = genes, Nurture = environment → they work together.

  • Think of it as “nurturing the nature” (genes and environment dance together).

Approaches

  • Molecular genetics: studies specific genes linked to traits (e.g., eye color).

  • Behavioral genetics: twin/adoption studies → estimates heritability of traits.

Historical Context

  • Buck v. Bell (1927) Supreme Court case legalized sterilization → later influenced Nazi eugenics policies.

Chromosomes & DNA Basics

  • 23 pairs of chromosomes → 23rd determines sex (XX = female, XY = male).

  • DNA made of 4 bases: Adenine, Thymine, Cytosine, Guanine.

  • ~20,500 genes in the human genome.

  • Mutations: can be inherited or new. Most harmless; sometimes beneficial for survival.

  • Nucleotides = base + phosphate + sugar.

Mendelian Inheritance

  • Gregor Mendel (pea plants) → dominant vs. recessive traits.

  • Genotype = genetic makeup (all genes, visible + hidden).

  • Phenotype = expressed traits (what you see).

  • Example: genotype carries blue + brown eye genes, phenotype may show only brown.

One Behavior, Many Genes

  • Polygenic inheritance: most traits/behaviors involve many genes.

  • Single-gene disorders: caused by one gene pair mutation (e.g., Tay-Sachs).

  • Pleiotropy: one gene influences many traits.

  • Generalist genes: same genes impact multiple related abilities.

Genetic Disorders

  • Single-gene disorders: recessive (both parents carry) or mutated dominant.

  • Sex chromosomes: Y chromosome shorter → males more vulnerable to recessive disorders.

  • Chromosomal abnormalities: extra or missing chromosome (e.g., Down syndrome = extra 21st chromosome).

  • Multifactorial inheritance disorders: genes + environment (e.g., depression, schizophrenia, ADHD).

Genetic Counseling & Testing

  • Who gets it? Parents >35, known family history, prior child with inherited disorder, certain ancestries (e.g., Tay-Sachs in Ashkenazi Jewish populations).

  • Tests:

    • Amniocentesis (after 15 weeks, needle extracts amniotic fluid).

    • Chorionic villus sampling (earlier, via cervix, collects placental cells).  Chorionic villus sampling can be done earlier in the pregnancy so the parents get the test results sooner

  • Ethical issues: privacy, informed consent, what to do with results.

Treatments & Management

  • Gene therapy: experimental, modifies or disables faulty genes.

  • Genome editing (CRISPR-like): cut/add/replace DNA; still limited.

  • Environmental management: diet, stress reduction → can affect gene expression (epigenesis).

  • Epigenesis: environment influences whether genes are “switched on/off.”

Behavioral Genetics

  • Goal: Understand genetic influence on behavior.

  • Heritability: Likelihood that a trait is passed from parent → offspring.

  • Adoption studies: Compare child’s traits to biological vs. adoptive parents.

    • Higher concordance with biological → genetic influence.

    • Higher concordance with adoptive → environmental influence.

  • Concordance rate: Degree of similarity for a trait between individuals.

  • Twin studies:

    • Monozygotic (identical): one zygote splits → 100% genetic overlap.

    • Dizygotic (fraternal): two zygotes → ~50% overlap (like siblings).

    • Higher concordance in identical vs. fraternal = stronger genetic influence.

  • Twins reared apart (Minnesota Study): Showed strong genetic effects, but controversy (some contact/relatives in same community).

Personality & Genetics

  • Big 5 traits show strong heritability:

    • Extraversion, Conscientiousness, Agreeableness, Neuroticism, Openness.

  • Genome-Wide Association Studies (GWAS) confirm genetic basis.

Interaction of Genes & Environment

  • Epigenesis: Environment can affect whether genes are expressed (“DNA is not destiny”).

  • Canalization: Degree to which gene expression can be shaped by environment.

    • Deeply canalized traits (e.g., early motor skills) → develop across cultures despite environment.

    • Less canalized traits (e.g., intelligence) → more sensitive to environmental input.

Behavioral Epigenetics

  • Chemical tags (e.g., maternal diet, BPA exposure, stress) influence gene expression.

  • Example: Mouse pups’ fur color + obesity risk tied to maternal nutrition.

  • Prenatal/early experiences matter: maternal stress → ↑ risk of depression, substance use in adolescence.

Gene–Environment Interactions

  • Passive: Parents provide both genes & environment (e.g., bookish parents → genes + book-filled home).

  • Active (niche-picking): Individuals seek out environments that match their genetic tendencies (e.g., child drawn to building/active play).

  • Evocative: Individual traits elicit responses from environment (e.g., outgoing child receives more social interaction).

✅ Key Takeaways for Quiz:

  • Know twin/adoption study logic (genetic vs. environmental influence).

  • Big 5 traits are highly heritable.

  • Define concordance rate, canalization, epigenesis.

  • Understand passive, active, evocative gene–environment interactions with examples.

  • Environmental influences (diet, stress, toxins) can alter gene expression.


Chapter 5

Prenatal Development

  • Stages of Prenatal Development

    1. Germinal Stage (conception → 2 weeks)

      • Begins with fertilization → zygote forms.

      • Zygote divides → blastocyst (hollow ball of cells) travels down fallopian tubes → implants in uterus.

      • 40–60% of conceptions fail before implantation; often unnoticed (no missed period).

    2. Embryonic Stage (weeks 2 → 8)

      • Amnion forms → protective sac around embryo.

      • Placenta develops: separates maternal/fetal blood; transfers nutrients/oxygen, blocks some infections (e.g., HIV).

      • Organogenesis: major organ systems laid down.

      • Cephalocaudal development: head develops first, then body (“head-to-toe” growth).

      • Most women discover pregnancy during this stage.

      • Ultrasounds used for monitoring.

    3. Fetal Stage (week 9 → birth)

      • Longest stage; rapid growth in size/weight.

      • Prenatal hormones guide brain/physical development.

        • Example: corpus callosum slightly larger in females.

      • Fetal breathing & swallowing develop.

      • Sensory development: touch first → taste & smell → hearing → vision (last to mature after birth).

      • Evidence of simple learning (e.g., newborn cry mimics mother’s language accent).

Pregnancy Overview

  • Trimesters: 1st (0–13 wks), 2nd (14–26 wks), 3rd (27 wks → birth).

  • Miscarriage: pregnancy loss before 20 weeks. The most common cause of miscarriage is chromosomal abnormality.

  • Infertility: failure to conceive after 1 year of regular unprotected sex.

  • Perinatal death: mother dies during or soon after childbirth—often linked to cardiovascular issues and lack of care.

Maternal Health & Risks

  • Prenatal care = crucial → improves outcomes.

  • Diet: balanced nutrition needed; malnutrition = leading worldwide teratogen.

  • Exercise: encouraged if already active, but avoid new intense/high-impact activities; hormone relaxin increases injury risk.

  • Abortion: intentional termination (medication or procedure); sometimes medically necessary (e.g., ectopic pregnancy).

Teratogens (agents that harm embryo/fetus)

  • Alcohol

    • No safe level; should be avoided entirely.

    • Fetal Alcohol Syndrome (FAS): distinct facial features (wide-set eyes, flat philtrum), smaller head/stature, cognitive & motor deficits.

    • Fetal Alcohol Spectrum Disorders (FASD): milder but still permanent cognitive/behavioral effects (often misdiagnosed as ADHD).

  • Tobacco


    4,000 chemicals; linked to low birth weight, developmental problems.

  • Drugs

    • Includes legal, prescription, OTC, recreational, illicit.

    • Ibuprofen unsafe; acetaminophen (Tylenol) generally safe.

    • Opioids: can cause Neonatal Abstinence Syndrome (NAS) → newborn withdrawal symptoms.

    • Cannabis: linked to reduced birth weight and risk of placental abruption (placenta tears from uterine wall → hemorrhage risk).

    • Cocaine: linked to pregnancy complications, later behavioral issues in child.

  • Diseases

    • E.g., German measles during embryonic stage → major organ/brain defects.

  • Maternal stress

    • Linked to higher rates of depression/PTSD in offspring.

  • Environmental toxins

    • Lead, mercury, pesticides, and other chemicals can damage development.

Key Facts to Memorize for Tests

  • 3 stages of prenatal development: germinal (0–2 wks), embryonic (2–8 wks), fetal (9 wks → birth).

  • 40–60% of conceptions fail before implantation.

  • Organogenesis occurs in embryonic stage.

  • Cephalocaudal development: growth from head downward.

  • Miscarriage: loss before 20 weeks.

  • Placenta blocks direct blood transfer between mother & fetus → limits some infections.

  • Touch develops first; vision last.

  • No safe alcohol use in pregnancy; FAS/FASD effects are permanent.

  • Opioids → NAS, cannabis → placental abruption, tobacco → low birth weight.

  • Maternal stress & malnutrition = significant risk factors. Maternal stress during a pregnancy seems to have its greatest impact if it occurs early in the prenatal period.

Birth Experience

3 Stages of Labor & Delivery

  1. Stage 1 – Labor:

    • Early → Active → Transition

    • Contractions start mild and spaced apart → become stronger/closer → transition = intense, almost no break between contractions.

  2. Stage 2 – Pushing / Delivery of Baby:

    • Natural urge to push once fully dilated.

    • Can last minutes to a couple of hours.

  3. Stage 3 – Delivery of Placenta:

    • Must be fully removed to prevent infection.

Newborn Assessment

  • Apgar Score: measured at 1 min & 5 min after birth.

    • A-p-g-a-r = Appearance (color), Pulse (HR), Grimace (reflexes), Activity (muscle tone), Respiration.

    • Each category 0–2 points → max 10.

    • Low score = medical intervention needed.

Infant States

  • Sleep: 2 states → Quiet & Active (REM = quiet sleep; much more REM than adults because of brain growth).

  • Wake: 4 states → Drowsy, Quiet-Alert, Active-Alert, Crying.

  • Crying: peaks around 6 weeks, then declines.

Risks for Newborns

  • Prematurity: birth before 37 weeks.

  • Low Birth Weight (LBW): ≤ 5 lb 8 oz (2.5 kg) even if full-term.

    • ↑ risk for behavioral/learning problems later and higher chance their own children will be pre-term (correlational, not causal).

  • NICU care: evolved from historical “child-hatchery” incubator model → now includes parental contact + kangaroo care (skin-to-skin) → improves outcomes.

  • Preterm/LBW babies can’t regulate temp, feeding, waste, breathing well → need incubators, IV/NG feeding, phototherapy for jaundice, etc.

Infant Mortality

  • Death within first year; highest risk = first 28 days (neonatal period).

SIDS – Sudden Infant Death Syndrome

  • Sudden, unexplained death of a healthy infant.

  • Still no clear cause.

  • Risk factors: prone sleeping (stomach), parental smoking, substance use, extreme parental obesity, unsafe co-sleeping.

  • Back-to-Sleep campaign lowered rates but hasn’t eliminated SIDS.

Abusive Head Trauma (Shaken Baby Syndrome)

  • Violent shaking → brain hits skull → swelling/bleeding, can be fatal.

  • Watch for sudden changes in feeding, sleepiness, unresponsiveness → seek ER care.

Transition to Parenthood

Mothers

  • Big hormonal shifts → emotional ups/downs postpartum.

  • Adjustment often smoother with strong partner/family/community support.

  • Sleep deprivation common because infants feed every 2–4 hrs.

Fathers

  • Couvade Syndrome:

    • Feigned couvade: culturally ritualized imitation of labor pain to distract “evil spirits.”

    • Psychosomatic couvade: real weight gain, mood swings, sleep changes in expectant fathers.

  • Often show drop in testosterone / rise in estradiol → more nurturing.

  • Support mother by attending appointments, sharing baby care, helping with supplies, feeding, night shifts, etc.

Family Adjustment

  • Baby’s survival depends on caregiver attention → natural intense parental focus.

  • Planning (e.g., splitting night shifts) eases stress.

  • Both positive & negative stressors; teamwork is key.

High-Yield Test Points

  • 3 Stages of Labor + Stage 3 = placenta delivery.

  • Apgar categories, score range (0-2 each, total 10), low = needs medical help.

  • Sleep/Wake states of newborn, crying peaks ~6 weeks.

  • Prematurity: < 37 weeks; LBW: ≤ 5 lb 8 oz.

  • First 28 days = highest mortality risk.

  • Back-to-Sleep → reduced SIDS; risk factors still remain.

  • Kangaroo care helps preterm/LBW infants.

  • Shaken Baby = brain injury from violent shaking.

  • Couvade syndrome (feigned vs psychosomatic) & hormonal shifts in fathers.

  • Maternal support + shared caregiving improve adjustment and infant outcomes.

Between 1965 and 2016, the amount of time that men spent in caring for a newborn tripled

Cesarean sections account for one-third of all U.S. births United States hospitals.

Chapter 6

Brain development

  • Hemispheres & lateralization

    • Two hemispheres; corpus callosum connects them.

    • Lateralization = functions lean to one side (e.g., right-handed → stronger left-hemisphere motor control).

  • Major structures & functions

    • Brainstem: breathing, heart rate.

    • Cerebellum: balance, coordinated movement.

    • Cerebral cortex: higher cognition; protracted development into ~age 25.

    • Amygdala: emotion.

    • Hippocampus: memory encoding.

    • Myth check: we use >10% of our brain; brain ≈ 20% of metabolic energy.

  • Plasticity

    • Brain changes with experience.

    • Romanian orphanage data: adoption ≤6 months → minimal deficits; longer deprivation → lower cognitive outcomes.

  • Neurons & synapses

    • Born with many neurons; pathways sculpted by experience.

    • Connections between nerve cells are called synapses


  • Axon releases neurotransmitters; dendrites receive.

  • Synaptogenesis rises with experience; synaptic pruning removes unused connections (energy efficiency).

  • White matter & myelination

    • Myelin = fatty sheath on axons → faster conduction.

    • Adequate fat in early nutrition supports myelination.

  • Experience-expectant vs. experience-dependent

    • Expectant: brain expects universal input (e.g., language). Missing critical-period input → lasting loss (Genie case).

    • Dependent: extra practice refines circuits (e.g., violinists show denser motor maps for the fingering hand).

  • Neurodevelopmental & psychiatric conditions

    • Cerebral palsy: motor/posture impairment; variable severity.

    • Autism spectrum disorder (ASD):

      • Research angles: (1) structure, (2) function, (3) connectivity (broader, atypical activation networks).

      • Early intervention (pre-school) with IFSP/IEP, speech/behavioral/OT → best outcomes.

      • Neurodiversity: support varied sensory/learning needs (quiet spaces, predictable routines).

    • Schizophrenia:

      • Rare (~≤1%); onset adolescence–30s.

      • Dx: ≥1 month prominent symptoms (e.g., hallucinations).

      • Lifelong management; not a “death sentence,” but serious.

Sensory development

  • Vision

    • Newborn best focus: 8–12 inches; face preference.

    • Adult-like acuity develops within the first year.

  • Hearing

    • Functional before birth; prenatal exposure to maternal physiological sounds and voices.

  • Smell & taste

    • Present prenatally; newborns prefer mother’s milk scent.

    • Prenatal flavor exposure influences later preferences (carrot-juice studies).

  • Touch & pain

    • Newborns feel pain; soothing (sweet solution, caregiver contact) reduces distress.

  • Cross-modal perception

    • Integrating senses (e.g., identify apple vs. orange by touch/smell/taste with eyes closed).

Body growth & puberty

  • Changing proportions

    • Infant head ≈ ¼ of body length; trunk/limbs catch up across childhood.

  • Teeth

    • Primary and permanent teeth develop under gums; eruption varies (~age 5–7 for first permanent).

  • Pre-pubescence & puberty

    • Pre-pubescence: hormonal shifts before physical signs.

    • Puberty: capacity for reproduction; sequential emergence of traits.

  • Timing terms

    • Typical pre-pubertal start around ~8.

    • Precocious puberty: <8 (girls) or <9 (boys).

  • Primary vs. secondary sex characteristics

    • Primary: reproductive organs (uterus/ovaries; testes/penis) mature.

    • Secondary: breast development, body/pubic/axillary hair, voice change, etc.

  • Menarche

    • First menstrual bleeding = evidence of ovulation cycle onset. Pregnancy possible before first period (ovulation precedes bleeding).

  • Early maturation risks

    • Earlier-appearing youth may face mismatch (adult treatment, child cognition) → ↑ risk for coercion, risk-taking (sex, substances).

    • Influences on timing: genetics, endocrine disruptors, chronic stress/trauma (can hasten onset).

Motor development

  • Reflexes (born with; most fade)

    • Sucking (~fades ~2 mo), Moro/startle (2–3 mo), Stepping (early months), Crawling reflex, Gag/Blink persist.

    • Persistence past expected windows → flag for peds eval.

  • Principles of motor development

    • Cephalocaudal: head → toe control.

    • Proximodistal: center (trunk) → outward (limbs → fingers).

    • Gross (large muscles: roll, sit, crawl, walk) develops before fine (pincer, drawing, handwriting).

    • Myelination of motor pathways underlies rapid gains.

  • Environment matters

    • Opportunities (tummy time, safe floor space, playgrounds) + caregiver encouragement accelerate practice and mastery.

    • Increased mobility boosts exploration and attachment behaviors (approach caregivers).

  • Developmental coordination issues

    • Delays/absence in expected milestones (crawl/walk/jump/pedal) → consider PT/OT.

Nutrition

  • Breastfeeding

    • Colostrum first: nutrient-dense, easy to digest; transitions to mature milk.

    • Benefits: immune, cognitive, bonding, and health benefits for infant and lactating parent. Lactation support often needed.

  • -An advantage of being breastfed for an infant is that breast milk contains antibodies from the mother that can help fight off infections

  • If not breastfeeding: formula is acceptable; priority = adequate intake.

  • Healthy eating in childhood

    • School meals help access, but can be processed; encourage fruits/veg, limit sugary drinks (e.g., chocolate milk).

  • Food allergies

    • Common: milk, soy, wheat; tree nuts/peanuts may persist lifelong; earlier onset → more likely chronic.

    • Many reactions are non-anaphylactic but still require avoidance; schools restrict food sharing.

  • Adolescent choices

    • More autonomy → more discretionary foods.

    • Family food rules (even one, like “veg at every dinner” or “no soda at home”) correlate with better choices.

  • Malnutrition & obesity

    • Global infant killer: wasting/marasmus.

    • U.S.: rising childhood obesity → tracks into adulthood; ↑ risk CVD, T2D.

  • Eating disorders

    • Anorexia nervosa: energy restriction; serious cardiovascular risks.

    • Bulimia nervosa: binge + purge; dental enamel erosion is a clinical clue; both have significant health risks.

High-yield examples & “gotchas”

  • Lateralization/handedness: right hand ↔ left hemisphere motor cortex.

  • Critical period for language: severe early deprivation → persistent grammar/syntax deficits (Genie).

  • Experience-dependent: instrument practice remodels motor cortex maps.

  • Pruning metaphor: like trimming a rose bush—keeps active pathways, drops unused.

  • Menarche misconception: pregnancy possible before first period because ovulation precedes the first bleed.

  • Precocious puberty cutoffs: Girls <8, Boys <9.

  • Reflex red flags: Moro beyond ~3 months or persistent primitive reflexes → evaluate.

  • Myelin & fat: early diet must include adequate fat for myelination.

  • ASD: earlier services → better language/adaptive outcomes.