Physical Development

Human chromosomes

  • 22 pairs (autosomes)
  • 1 pair of sex chromosomes
    • Eggs: 22 chromosomes + x
    • Sperm: 22 chromosomes + x or 22 chromosomes + y
    • Determines biological sex
    • XX = female, XY = male

Genetic material

  • Chromosome: one large piece of DNA with thousands of genes on it
    • Abnormalities: trisomies
    • Three copies of a chromosome
    • Imbalance in gene products
  • Gene: segment of DNA that codes for a protein
    • Protein does jobs in the cells
    • 2 copies of each
    • Dominant allele (version of gene): only needs one copy for trait to be expressed
    • Recessive allele: needs two copies to be expressed
    • Ex) Disease inherited with recessive pattern: PKU
      • PKU → can’t ingest phenylalanine, must inherit from both parents
  • Each cell has identical DNA
    • Functionally different based on gene expression

Prenatal development

1) Germinae Stage

  • Fertilization to implantation (10 days)

2) Embryonic Stage

  • ~10 days to 9 weeks
  • Placental forms
  • Major organs form and begin to function

3) Fetal Stage

  • ~9 weeks to birth

Teratogens: environmental agents that can cause birth deffects

  • Most dangerous during embryonic stage because of organogenesis

Fetal Alcohol Syndrome

  • Depresses central nervous system of fetus
    • Kills brain cells
    • FAS babies are underweight and have cognitive defects

Maternal smoking

  • Restricts blood flow to fetus → underweight, poor brain development

Reflexes

  • Advantageous → promote survival
  • Genetically encoded

Moro Reflex

  • When startled → splay arms and legs outward
    • Due to noise or feeling like falling

Grasping Reflex

Rooting Reflex

  • Stroke baby’s cheek → turn towards what is stroking

Babinski Reflex

  • Stroke bottom of foot → toes splay out

Maturation

  • Orderly, biologically sequence of development
    • Ex) Sitting before crawling
  • Genetically determined
  • Order is not affected by experience
  • Timing affected by environment
    • Ex) Poor nutrition

Neural development

  • At birth, most neurons are present
  • Rapid increase in number of synapses
  • Pruning begins in puberty through adulthood

Continuity vs. Stages

  • Continuity: single continuous process of development
  • Stages: fixed sequence with each stage building on previous

Critical periods

  • Period in development where if skill is not acquired, normal development cannot occur
    • Ex) Language

Sensitive periods

  • In development, time where child is particularly receptive to learning a skill
    • Ex) Potty training

Longitudinal studies

  • Follow same group of people over many years → assessed on same variable

Cross-sectional studies

  • Multiple age groups are assessed on single occasion on a variable

Natural selection

  1. Variations exist → heritable
  2. Selection pressure (competition for survival)
  3. If organism survives and reproduces → pass on genes
  4. Organisms whose traits allow survival will reproduce and pass on their genes the most
  5. Proportion of individuals in population with advantageous trait will increase

Universality → mate choice

  • For females: older, affluent
    • Better able to care for children
  • For males: young, healthy looking, chaste
    • Fewer issues with childbirth/birth defects
    • More babies
    • More certain that it is their baby