Genetic Inheritance, Epigenetics & Early Development – Support Session Notes

Session Context

  • Second live support session for the course “Lifespan Development.”
  • Graduate Assistants (GAs):
    • Alex Joseph – pronouns he/him/they, background in Criminal Justice (B.S.), Public Administration (M.P.A.), 10 yrs in non-profit sector, avid reader (48 books/2 yrs), currently writing a book.
    • Nicole Lanker – originally Boston, now Arizona; PsyD student (started practicum), full-time employee, parent, fitness enthusiast.
  • Recording available for later review.
  • Participation norms: be professional, positive, active, growth-minded, aligned with Capella’s code of conduct.
  • Accessibility: disclose any accommodation needs in any preferred manner.

Agenda Overview

  • Re-introduction of GAs
  • Learning topics & objectives
  • Pulse-check question
  • Core content:
    1. Genetic inheritance (dominance patterns + hereditary disorders)
    2. Epigenetics (attachments, age, disease)
    3. Early development:
    • Prenatal stages (0–9 mo)
    • Early brain development
    1. Telomerase, teratogens, fetal-alcohol syndrome
  • Final reflection & reminders.

Ice-Breaker Prompt

  • Chat prompt: “Name a song/smell/food that reminds you of childhood and why.”
    • Examples shared: smell of hamburgers & hotdogs (summer + amusement parks), smell of pool chlorine (swim memories), first snowfall at Christmas (East Coast nostalgia).

Learning Objectives

  1. Genetic Inheritance
    • Distinguish complete, incomplete, co- & mixed dominance.
    • Relate gene patterns to disorders & diseases.
  2. Epigenetics
    • Link to attachment, aging, disease processes.
  3. Early Development
    • Chart prenatal months 0–9.
    • Identify 5 & 7 recognized stages of brain development.
  4. Health vs. Harmful Brain Development
    • Role of telomerase, teratogens, fetal-alcohol syndrome.

Pulse-Check Question

“Which factor do you think has the greatest impact on fetal development – nutrition, substance use, maternal stress, or environmental factors?”

  • Majority view: all important; many singled out maternal stress or substance use.
  • Recognition that “environmental factors” can subsume the other three.

Foundations of Development

1. Genetic Inheritance

  • Definition: transmission of DNA-based traits from parents to offspring.
  • Every gene = 2 alleles (one maternal, one paternal).
  • Dominant allele → expressed whenever present.
  • Recessive allele → expressed only if paired with another recessive.
  • Genotype = allele combination; phenotype = observable trait.
  • Homozygous: AAAA or aaaa; Heterozygous: AaAa.
Complete Dominance
  • Dominant masks recessive; phenotype always dominant if at least one capital allele present.
  • Eye-color example:
    • BB = brown (dominant), bb = blue (recessive).
    • Punnett Square (two BbBb parents):
    • BB,Bb,Bb,bbBB, Bb, Bb, bb → 75%75\% brown, 25%25\% blue.
    • Expressed mathematically:
      P(brown)=0.75,P(blue)=0.25.P(\text{brown}) = 0.75, \quad P(\text{blue}) = 0.25.
Incomplete Dominance
  • Neither allele fully dominates; heterozygote shows blended phenotype.
  • Snapdragon: RRRR (red) × WWWW (white) → RWRW (pink).
  • Note: no recessive alleles involved—both parental traits are dominant but only partially expressed.
Codominance & Mixed Dominance
  • Codominance: both parental phenotypes appear side-by-side.
    • Camellia shrub flowers show red & white patches.
  • Mixed/Multiple Dominance: heterozygote simultaneously expresses both dominant alleles.
    • Human ABO blood:
    • IAI^{A} & IBI^{B} are codominant → type ABAB expresses both antigens.
    • IOI^{O} is recessive; thus IAIOI^{A}I^{O} → type A, IBIOI^{B}I^{O} → type B.
Hereditary Disorders
  • Transmission patterns:
    1. Autosomal dominant
    2. Autosomal recessive
  • Carrier state: Phenotypically normal but possesses 1 diseased recessive allele.
  • Two carrier parents (Aa × Aa):
    P(unaffected)=25%,  P(carrier)=50%,  P(affected)=25%.P(\text{unaffected}) = 25\%, \; P(\text{carrier}) = 50\%, \; P(\text{affected}) = 25\%.
  • Sample conditions: Down syndrome, fragile X, Turner & Triple-X syndromes, diabetes, Alzheimer’s, arthritis, autism, various cancers.
  • Real-life anecdote: GA’s mother developed gestational diabetes → child later became pre-diabetic (environment + genetics).

2. Epigenetics

  • Study of heritable yet reversible modifications that regulate gene expression without altering DNA sequence.
  • Common mechanisms:
    • DNA Methylation (–CH₃ groups) – tends to silence genes (on/off switch).
    • Histone modification – alters chromatin tightness (dimmer knob).
  • Epigenome = “software” dictating how DNA “hardware” is read.
  • Tags evolve across life stages (embryo → puberty → adulthood → aging).
  • Influences: diet, stress, toxins, smoking, exercise, social context.
Twin/Clone Thought-Experiment (video summary)
  • Identical genome, divergent life histories → distinct epigenetic punctuation (spaces & commas).
  • Methyl groups + histone changes create differing phenotypes (height, fitness, disease risk).
  • Some parental tags escape erasure in early embryogenesis → inter-generational transmission.
    • Historical Swedish famine–feast records show nutrition swings in grandparents affected grandchildren’s longevity (≈ 6 yrs difference).
Nature vs. Nurture Revisited
  • Epigenetics evidences bidirectional interplay: environment writes temporary or permanent notes on genetic script.
  • Practical takeaway: lifestyle choices (nutrition, stress management) can modulate inherited risk profiles.
Epigenetics & Attachment
  • Quality of parental care shapes epigenetic regulation of stress-response genes (e.g., glucocorticoid receptor).
  • Strong, consistent caregiving ⇒ healthier hypothalamic–pituitary–adrenal (HPA) calibration, better emotional regulation.
  • Potential reversibility offers therapeutic avenues (e.g., enriched environments, supportive interventions).
Epigenetics & Disease
  • Pathogens may alter host methylation to dampen immunity (e.g., Mycobacterium tuberculosis silences IL12BIL12B gene).
  • Cancer: aberrant methylation patterns—global hypomethylation but hypermethylation at tumor-suppressor promoters (e.g., BRCA1BRCA1).
    • Screening example: Cologuard detects colorectal-cancer-specific methylation signatures in stool samples.
    • Positive stool test ⇒ colonoscopy confirmation.

Early Human Development

Prenatal Milestones (video "Olivia")

  • Week 1: implantation begins.
  • Day 22 (~3 wk + 1 d): first detectable heartbeat.
  • Week 4: limb buds.
  • Week 5–6: spontaneous & reflexive movements; brain waves present; ossification starts.
  • ≈ 7.5 wk: hands can meet; individual fingers/toes separate; hiccups begin.
  • Week 9: transition from embryo → fetus (~1 billion cells).
  • Weeks 9–12: thumb-sucking, grasping, facial touching, audible sighs & stretches; scattered taste buds mature.
  • Quickening (maternal perception of movement): 14–1814\text{–}18 wk.
  • Week 18: early laryngeal (voice box) movement—“silent practicing.”
  • Week 20: “limit of viability” with intensive medical support.
  • Week 27: eyes respond to light; fetus recognizes parental voices & familiar sounds.
  • Birth follows signal cascade when ready.

Early Brain Development & Plasticity

  • Neurodevelopment is experience-dependent: every sensory, motor, emotional, cognitive input sculpts synaptic architecture.
  • Experience-Expectant Plasticity:
    • Universal inputs (visual patterns, language exposure) during critical periods build baseline circuits.
  • Experience-Dependent Plasticity:
    • Individual learning/events overlay unique synapses & skill sets (e.g., musical training).
  • Neuroplasticity scales:
    1. Macroscale – regional activation networks
    2. Mesoscale – long-range & local circuitry
    3. Microscale – neuron & synapse modification.
  • Maladaptive plasticity underlies many neurodevelopmental, acquired & degenerative disorders.
  • Caregiver/educator role: provide enriched, diverse, nurturing environments to optimize synaptic pruning & strengthening.

Health vs. Harm in Brain Development

  • Telomerase: enzyme maintaining telomeres; protective against cellular aging; stress can accelerate telomere shortening.
  • Teratogens: environmental agents causing prenatal harm (alcohol, nicotine, certain meds, radiation, infections).
  • Fetal-Alcohol Syndrome (FAS): spectrum of growth deficits, facial dysmorphology, CNS impairment ⇒ underscores substance-use impact.

Integrative Connections & Implications

  • Genetic blueprint + epigenetic notes + experiential inputs = holistic developmental outcome.
  • Ethical/practical takeaway:
    • Support healthy prenatal conditions (nutrition, low stress, toxin avoidance).
    • Foster secure attachments & enriched learning contexts.
    • Public-health policy can leverage epigenetic knowledge for prevention (anti-smoking, nutrition programs).
  • Research frontier: targeting reversible epigenetic marks for therapeutic benefit (e.g., cancer demethylating agents, stress-response modulation).

Key Numerical References & Equations

  • Punnett probabilities for two heterozygous brown-eye parents:
    P(brown)=0.75,  P(blue)=0.25P(\text{brown}) = 0.75, \; P(\text{blue}) = 0.25
  • Carrier × carrier hereditary disease outcome:
    25% unaffected:50% carrier:25% affected{25\% \text{ unaffected}} : {50\% \text{ carrier}} : {25\% \text{ affected}}
  • Grand-parental feast–famine Swedish cohort: premature mortality shift ≈ 6 yr6\text{ yr}.

Study Tips & Reflection Prompts

  • Re-draw Punnett Squares for various dominance scenarios (eye color, blood type).
  • List 3 lifestyle choices that could meaningfully alter one’s epigenome; predict possible gene pathways affected.
  • Map prenatal milestones on a timeline; annotate teratogen-sensitive windows.
  • Contrast experience-expectant vs. experience-dependent plasticity with real-life examples (e.g., language emergence vs. learning violin).
  • Reflect: How might knowledge of epigenetic inheritance change public-health messaging or personal decisions?