L2: Hereditary and Prenatal Development

Intro

• hereditary influences on development

• influences of genes on probability/sensitivity on neurodevelopment

• genes interact with environment + experience + timing (when genetic changes happen)

• case paper - to avoid genetic determinism

Introduction to Genetics (Zygote)

• father’s sperm + mother’s ovum = zygote

• 46 chromosomes total

• 23 from each parent

• Every cell in your body traces back to this single cell.

The Role of Genes

• Each chromosome contains genes.

  • Made up of DNA

  • The chemical code that supports development

  • Shaped like a double helix

  • Has the ability to replicate + respond to signals, of which give rise to development for a child to be flexible rather than fixed (for recovery, dev, etc.)

• genes from the basis of hereditary

Hereditary Transmission - Mitosis

• Mitosis begins after fertilization. (allows single cell → complex organism of many cells; although cells have same genetic material, they do not become same cell type → same genes therefore does not lead to same developmental outcome)

• cells divide to support growth + repair

Hereditary Transmission - Meiosis

• Meiosis- produces reproductive cell (sperm, egg), exchanges genetic material thru crossing over, creating new combo of genes - a major reason why siblings differ in temperament, cognition, etc. even from same parent

• Genetic diversity - diff starting points - interact differently w env over time

• Crossing over: Genes from a maternal chromosome “cross over” to the paternal chromosome and vice versa. Note that the 23rd pair of chromosomes for the male consists of one elongated X chromosome and a Y chromosome that is noticeably smaller, whereas the 23rd pair for the female consists of two X chromosomes

Multiple Births: Identical vs. Fraternal Twins

• Multiple births: twins

  • Monozygotic (identical): a zygote that divides to form two genetically identical individuals (share all genes)

  • Dizygotic (fraternal): occurs when two ova are released simultaneously and each is fertilized by a different sperm (share half of genes)

• Identical, or monozygotic, twins (left) develop from a single zygote. Because they have inherited identical sets of genes, they look alike, are the same sex, and share all other inherited characteristics → if identical twins are the same = genetic influence; but their differences highlight important of env influences

• Twins provide a natural experiment for studying heredity and environment → helps separate genetics + env influences

Determining Biological Sex: The Role of Chromosomes

• Male or female?

• The 23rd pair of chromosomes:

  • Males have X and Y chromosomes

  • Females have X and X chromosomes

• Sex of child determined by father’s sperm

Functions of Genes in Development

• Genes direct production of amino acids necessary for forming new cells

• Guide cells to develop different parts of body (differentiation)

• Regulate pace and timing of development

  • May “turn on” or “turn off” other genes

• Impacted by environmental factors

Gene Expression and Inheritance Patterns

• Gene expression - whether a gene is active at a certain time (simplest model)

• Alleles influence many characteristics

  • One pair of genes

  • One member from mother, one from father

• Simple dominant–recessive inheritance (e.g., eye colour)

  • Some alleles are stronger than others.

    • Dominant alleles will always express themselves if they are present.

    • Recessive alleles will only express themselves if both alleles in the pair are recessive.

Allele Combinations: Homozygous, Heterozygous, and Codominant

• If two alleles are homozygous

  • they are both dominant or both recessive.

• If two alleles are heterozygous

  • one is dominant and one is recessive

• If two alleles are codominant

  • both alleles are expressed simultaneously.

  • e.g., AB bloodtype

Examples of Dominant and Recessive Traits

• Most psychological traits are polygenic and not determined by single genes

Sex-Linked and Polygenic Inheritance

• Sex-linked inheritance

  • Characteristics associated with genes on sex chromosomes

  • Most on X chromosome

    • Making males more susceptible to recessive X-linked traits (no second X chromosome to buffer/compensate) → hence some conditions more likely for males

• Polygenetic inheritance

  • Characteristics influenced by many pairs of alleles

  • many psych characteristics fall under this category

  • shows that many outcomes are probabilistic rather than predetermined

Epigenetics: Modifying Gene Expression

• Epigenetics: a modification of gene expression that has no effect on the DNA (influences activation of genes)

  • Can affect subsequent generations under specific circumstances

  • gene expression responsive to experience (env, diet, exposure to toxins, caregiving envs, etc.)

• Example: environmental factors like stress, diet, or exposure to toxins can lead to epigenetic changes that might affect offspring (can transfer b/w generations)

Hereditary and Congenital Disorders

• Babies may have problems at birth due to hereditary (genetic) or prenatal environmental influences

• Hereditary disorders are passed from parents to offspring

• Congenital problems are present at birth but not always apparent at birth (e.g., autism, seizures)

• Present at birth ≠ detected at birth

Causes of Chromosomal Abnormalities

• How do chromosomal abnormalities occur?

  • During cell division in meiosis (production of eggs + sperms), distribution of chromosomes may be uneven (nondisjunction)

    • separation may not be even → gametes

  • May also occur through mutation (changes in genetic material caused by error in replication process or thru exposure to env hazards)

  • Most abnormalities are lethal.

  • Some are not, and some babies are born with +1 or −1 chromosome. (leads to recognizable dev pattern/visible in child at birth)

Hereditary Disorders

Sex chromosomes

• Female abnormalities

  • Turner syndrome: XO

  • Poly-X syndrome: XXX, XXXX, or XXXXX

• Male abnormalities

  • Klinefelter syndrome: XXY or XXXY

  • Supermale syndrome: XYY, XYYY, or XYYYY

• those w developmental disorder may have healthy lives but need support etc.

Autosomal Abnormalities: Down Syndrome

• Autosomes

  • First 22 pairs of chromosomes (not involved in sex determination)

• Autosomal abnormalities

  • Down syndrome (trisomy 21) most common

  • Extra 21st chromosome

  • Intellectual disability - reach key dev milestones but at a slower pace

  • Distinctive physical features

  • Risk increases with age of mother - genetic influences on meiosis process rather than env influences?

Genetic Abnormalities: Recessive and Dominant Alleles

• Genetic abnormalities often associated with recessive alleles

  • Recessive disorder = child inherits affected allele from both parents who are healthy carriers

    • Cystic fibrosis

    • Diabetes

    • Hemophilia

    • Parents often healthy; both must be carriers

    • all more common in males due to x-linked inheritance

• Some genetic abnormalities associated with dominant alleles

  • Huntington’s disease

  • Parent contributing allele has the disorder

Genetic Counselling and Detection of Hereditary Disorders

• Genetic counselling: professional service that helps prospective parents estimate the likelihood of hereditary or chromosomal disorders

• Especially relevant for:

  • Older parents

  • Families with a history of genetic disorders

  • Couples who have previously had an affected child

• Key tools used

  • Pedigree analysis: family history across generations

  • Blood and DNA tests: identify carrier status ▪ Screening tests: assess risk, not certainty

Prenatal Detection Techniques

Amniocentesis (15–22 weeks)

• Analyzes fetal cells in amniotic fluid

• Detects chromosomal and genetic disorders

• Small miscarriage risk (Approx. 1 in 400)

Chorionic villus sampling (CVS) (10–14 weeks)

• Earlier detection than amniocentesis

• Slightly higher miscarriage risk (1–2%)

Non-invasive prenatal testing (NIPT)

• Blood test using placental DNA

• Very high accuracy for trisomy 21 (down syndrome)

• Screening Test (not diagnostic)

• No risk to fetus

• Positive NIPT results require confirmation with diagnostic testing

Ultrasound

• Detects physical abnormalities

• Does not test chromosomes directly

Treating Hereditary Disorders (review)

• Treatment approaches

• Dietary interventions

  • Phenylketonuria (PKU) managed through early and sustained dietary control - genetic disorder that cannot break down phenylalanine

  • Example of how early intervention alters developmental trajectories

• Fetal surgery (rare, final option)

  • Corrects life-threatening abnormalities before birth

  • Still experimental; ethical risks involved

• Genetic engineering (replacing affected genes w healthy ones to correct error)

  • Somatic gene therapy: affects the individual only

  • Germline gene therapy: affects future generations (highly controversial)

Hereditary Influences on Behaviour - review

• Behavioral genetics examines how genes and experience jointly shape behavior

• biological predispositions + environmental experiences

• Which behaviors show genetic influence? •How do environments amplify, suppress, or redirect genetic tendencies?

Genotype and Phenotype: Hereditary Influences on Behaviour

• genotype (inherited genetic potential) is expressed thru phenotype (observable traits & behaviours)

Hereditary Influences on Behaviour (review)

• Heritability: Refers to population-level variability, not individuals

  • A high heritability does not mean a trait is fixed or unaffected by environmental influence

• Methods to determine heritability

  • Selective breeding experiments (animals): shows genetic contribution

    • Tryon’s “maze bright” and “maze dull” rats (rats bred for ability to navigate maze; bright rats improved over generations → shows genetic basis for maze running ability)

  • Family studies - compare resemblance among relatives (trait comparison among family members shows similarities)

Family Study Methods in Behavioral Genetics

• Twin design

  • Researchers compare maternal + fraternal twins - if identical twins are more similar, genetics play roles in trait

  • ?

  • Are identical twins raised up together more similar than fraternal twins raised up together?

• Adoption design

  • Are adopted children similar to biological parents or adopted parents?

  • If child is more similar to parents, there is genetic influence

  • Adopted children similar to adoptive parents, suggests an env influence

• Concordance rates are calculated

  • Percentage of pairs of people in which both members display a trait (identical twins often discordant for many traits…)

Environmental Influences on Behavior

• Two influences examined

• Non-shared environmental influences: Experiences unique to individual, not shared by other members of family in same environment

• Shared environmental influences: Experiences common to all family members in same environment (e.g., family socioeconomic status, parenting styles, diets)

Heritability and Inheritance - review

• Heritable does not equal inherited.

• heritability - how much variation in a specific trait in the pop can be contributed to by genetics

• does not mean it can be inherited by individual (cognitive abilities, illnesses, etc.) but genetic factors can influence greatly

• ADHD is heritable, but does not mean a child would inherit ADHD from their parents, as research shows that parenting style, education, and stress plays a role in whether or how ADHD manifests

Gene-Environment Interactions: Canalization Principle

Canalization principle: Genes restrict development to a small range of outcomes. Meaning that some traits are highly regulated by genes and are less influenced by the environment.

• basic motor skills, language development, occurs

• e.g., babbling + walking in infants (walking around the same age regardless of environmental factors (cultures, areas, etc.))

Range-of-Reaction Principle

Genes set boundaries for a range of phenotypes (possible outcomes) based on environment, and the environment determines where within that range an individual will fall (enriched environment (within highest range) vs. impoverished environment (within lowest range))

• Child’s height has a genetic range, but factors like nutrition or health can influence whether they reach the upper or lower end of that genetic potential

Genotype and Environment Correlations

Genotype and environment may be correlated.

• Passive genotype/environment correlations: when parents provide both genes and environments to their children (parents who are musicians, likely that child inherits their musical talent, and they may grow in a much more musical environment)

• Evocative genotype/environment correlations: when a child's genotype is prompted the environment. (review)

• Active genotype/environment correlations: when a child actively selects environments that match genetic tendencies.(seek envs that enriches + supports their talents (e.g., sports))

Contributions and Criticisms of the Behavioural Genetics Approach

Contributions

• Many traits are influenced, at least in part, by genes

• Epigenetic re-modelling plays role in phenotype plasticity (env can impact plasticity) - review plasiticity

Criticisms

• Behavioral genetics often describes how much genes and environment matter, but less clearly explains how they interact across development.

• Many behavioural genetic findings come from population averages and may not apply directly to individuals. (overgeneralization)

Prenatal Development Stages

• Germinal period or the period of the zygote

• Period of the embryo

• Period of the fetus

Germinal Period

Germinal period or the period of the zygote

• From conception to implantation in uterine wall

• Zygote travels down the fallopian tube

• Cell division occurs in preparation for implantation

• Most fertilized eggs never implant successfully

Period of the Embryo (Embryonic)

Period of the embryo (From week 3 to week 8)

• Formation of major body structures

• Development of three cell layers:

  • Ectoderm: Nervous system and skin

  • Mesoderm: Muscles, bones, circulatory system

  • Endoderm: Digestive system and lungs

• Development of placenta and umbilical cord - very vulnerable stage of development

Period of the Fetus

Period of the fetus (From week 9 to birth)

• Rapid growth and organ development

• By third month: Movement, digestion, urination, and sex organ formation

• Second trimester: Refined movements (kicking, thumb sucking)

• Third trimester: Organ system maturation and weight gain

• Age of viability: Weeks 22–28 (survival outside the womb)

• Birth typically between weeks 38 and 41

Environmental Influences on Prenatal Development

• Environmental factors affect prenatal development.

• Teratogens (viruses, drugs, chemicals, radiation) - embryonic period most sensitive to

• Environmental hazards (air pollution; water contamination)

• Maternal characteristics (Nutrition, emotional well-being, age)

• diagram - dark purple most sensitive periods, light purple less sensitive to teratogens

Sensitive Periods in Prenatal Development

• Each developing structure has a sensitive period.

  • A time when it is particularly susceptible to be damaged from teratogens + alcohol, etc.

  • Recall rapid development during embryonic period

• Once fully formed, body parts are less susceptible to damage. (higher risk for behavioural/functional abnormalities rather than physical abnormalities that are more likely to occur early on)

Maternal Diseases

• Rubella Disease (German weasels)

  • Most dangerous in first trimester

  • Effects include blindness, deafness, cardiac abnormalities, intellectual disability

• Toxoplasmosis Infection

  • Caused by a parasite acquired from undercooked meat or handling feces from cats

  • Effects include brain damage, vision loss in first trimester; miscarriage thereafter

Sexually Transmitted Diseases/Infections

• Syphilis: not dangerous until 18th prenatal week

  • Effects include eye, ear, bone, heart defects or brain damage, or miscarriage

  • can be cured through antibiotics for mother (but may lead to still birth)

• Genital herpes: most infectious at birth (thru birth canal via natural birth)

  • Effects include death, blindness, brain damage, neurological disorders

• HIV/AIDS: screening and antiretroviral treatment have reduced prenatal transmission to 2% (in NA and Europe).

  • Effects of exposure to HIV in developing countries include low birth weight, impaired early growth, impaired psychomotor and cognitive development, and immune issues.

Thalidomide and Diethylstilbestrol (DES): Historical Lessons on Teratogens

• 2 historical drugs that were first believed to be safe but are actually harmful

• Thalidomide (unpredictable risks)

  • Originally marketed to relieve morning sickness among pregnant women

    • Lab tests with rats showed no effect on fetus

  • Harmful when taken early in human pregnancy

    • Many babies born with severely deformed eyes, ears, noses, hearts, and phocomelia (underdeveloped limbs)

  • Yet, many showed no effect at all → risk is unpredictable

• Diethylstilbestrol (DES) - used for pregnancy support and cancer treatment

  • Effects not apparent until early adulthood (reproductive system cancers or fertility issues for children)

Alcohol and Fetal Development: FASD and Its Impact

• Fetal alcohol spectrum disorder (FASD) - umbrella term for prenatal alcohol exposure, increases risk for the following:

  • Fetal alcohol syndrome (FAS)

    • Caused by heavy drinking

    • Effects include microencephaly (baby head’s smaller than expected bc brain did not develop properly/stopped developing), facial malformation, hyperactivity, seizures, intellectual and learning difficulties

  • Fetal alcohol effects (FAE)

    • Caused by moderate, social drinking

    • Effects include poor motor skills, attention problems, below-average intelligence

The Impact of Cigarette Smoking on Prenatal Development

• Cigarette smoking, introduces nicotine + CO2 into bloodstream for mother + child, affecting oxygen levels + nutrients?

  • Slows growth of fetus

  • Associated with low birth weight and increased risk of cleft lip with or without cleft palate

  • ↑ risk of miscarriage or of SIDS (sudden infant death syndrome)

  • Long-term effects less clear

    • Some studies report cognitive deficiencies, however,

  • strongly shaped by postnatal environment and caregiving.

The Impact of Illicit Drugs on Prenatal Development

• Cocaine → Premature births mean smaller babies, lower IQs

• Opioids (ex.Heroin, prescription Narcotics) → Increased neonatal death, born addicted, may recover

• Marijuana → prenatal exposure has been associated with emotional, behavioural, and academic problems

Radiation and Environmental Hazards in Prenatal Development

• Radiation: high exposure can result in serious physical deformities, intellectual disabilities, death (timing + dose important)

• Chemicals and pollutants: can cause physical deformities and intellectual disabilities

• these risks are probabilistic rather than deterministic

Maternal Diet and Its Impact on Fetal Development

• Diet - Weight gain of 11 to 14 kg recommended

• Malnutrition results in small babies.

  • May disrupt spinal cord development in first trimester

  • Leads to low birth weight in third trimester

• Adequate protein-calorie intake crucial to brain development

• Folic acid (folate) is crucial for neural tube development.

  • Spina bifida is a defect occurring during neural tube development.

Emotional Well-Being and Age Factors in Pregnancy

• The mother’s emotional well-being

  • ↑ chronic/severe stress (e.g., workplace stress, loss of a loved one) → ↓ birth weight → ↑birth complications

  • moderate stress may not be harmful + may support fetal development

• The mother’s age

  • Risks associated with teen mothers (premature birth, low birth weight associated w little prenatal care)

  • Risks associated with older mothers (above mid-30s) - increased risk of chromosomal abnormalities, etc.

• Protective factors such as social support can reduce prenatal stress effects.

Genetic Abnormalities and Healthy Birth Outcomes

• Most genetically abnormal embryos do not develop to term.

• Ninety-five percent of newborns are healthy.

• Many of the remaining 5% have minor congenital problems (minor, temporary, or treatable).

• Prospective parents can lower the odds of an abnormal birth by following practical suggestions (healthy lifestyle, stress management, avoiding harmful substances, prenatal care.

Reading - why read it? Central Developmental Claim + Evidence

Why Are We Reading This Paper?

• discussed 2 topics: Do prenatal experiences shape mental health? What does “risk” mean in developmental psychology?

Central Developmental Claim

• Prenatal conditions are associated with later mental health risk

• Effects are probabilistic, not deterministic

What Evidence Is Used?

• Correlational evidence b/w birth weight + later psychopathology and chronic illnesses

• Longitudinal human studies

• Epidemiological data

• Animal models

• Neurobiological research

What the Paper Does Not Claim?

• that prenatal stress causes mental illness (rather that it changes the risk trajectories)

• that effects are permanent or irreversible

• that there is only one single biological pathway

Common Misinterpretations!

• “Prenatal stress permanently damages children.”

• “Mothers cause children’s mental health problems.”

• “Prenatal experiences determine children's futures.”

Best Developmental Lens + Why this matters?

• Transactional / developmental systems perspective

  • development is plastic

  • transactional = relational, interactional

• Biology × environment × time

  • timing is important

• Increased sensitivity, not fixed outcomes