PSYC 2103-Chapter 2_Students

CHAPTER 2: GENES, ENVIRONMENT, AND DEVELOPMENT

  • Instructor: Dr. Sherman Valdosta State University

  • Course: PSYC 2103: Introduction to Human Development

  • Semester: Spring 2025 – In-Person

EVOLUTION AND HUMAN DEVELOPMENT

  • Species heredity:

    • Common genetic endowment shared by species influencing biological maturation and aging.

    • Accounts for universal patterns of development and aging.

  • Darwin's arguments:

    • Genetic variation exists within species.

    • Some genes promote better adaptation than others.

    • Natural selection:

      • Nature selects individuals with advantageous genes for survival and reproduction.

MODERN EVOLUTIONARY PERSPECTIVE

  • Ethology:

    • Understanding evolved behaviors in natural settings.

  • Evolutionary psychology:

    • Applies evolutionary theory to explain human thought and behavior.

  • Significance of biological evolution:

    • Development of a powerful, flexible brain enabling learning and adaptation.

LIFE HISTORY STRATEGIES

  • Slow life history strategy:

    • Evolves in safe, predictable environments.

  • Fast life history strategy:

    • Evolves in harsh, unpredictable environments.

  • Cultural evolution:

    • Inheritance of human characteristics across generations, adapting to changing conditions.

INDIVIDUAL HEREDITY: THE GENETIC CODE

  • Conception:

    • Occurs when an egg is fertilized by a sperm.

    • Each contributes 23 chromosomes, forming a zygote of 46 chromosomes.

  • Chromosomes:

    • Threadlike bodies in cell nuclei made of genes.

MITOSIS AND MEIOSIS COMPARED

  • Mitosis:

    • Begins at conception, continues throughout life.

    • Produces 2 identical cells with 46 chromosomes each.

  • Meiosis:

    • Males: Puberty onward, producing 4 sperm each with 23 chromosomes.

    • Females: Begins early prenatal, producing one ovum and three nonfunctional polar bodies, each with 23 chromosomes.

  • Accomplishments:

    • Mitosis: Growth and renewal.

    • Meiosis: Formation of reproductive cells.

GENETIC UNIQUENESS AND RELATEDNESS

  • Crossing over:

    • Exchange of chromosome parts during cell division increases genetic variability.

  • Identical twins:

    • Formed from one fertilized ovum dividing into two genetically identical individuals.

  • Fraternal twins:

    • Result from two separate ova being fertilized simultaneously.

DETERMINATION OF SEX

  • Sex chromosomes (23rd pair):

    • Males: XY (one X, one Y).

    • Females: XX (two X chromosomes).

    • Determines child’s sex.

GENOTYPE AND PHENOTYPE

  • Genotype:

    • Genetic makeup inherited by a person.

  • Phenotype:

    • Observable characteristics or traits of an individual.

  • Gene expression:

    • Activation of particular genes at specific times in various cells.

  • Dominant gene:

    • Expressed when paired with a recessive gene.

  • Recessive gene:

    • Weaker gene that can be overshadowed.

MUTATIONS

  • Mutations:

    • Changes in gene structure/arrangement resulting in a new phenotype.

    • Environmental hazards increase mutation chances.

    • Most mutations are spontaneous errors during cell division.

    • Fathers contribute approximately four times more new mutations than mothers.

CHROMOSOME ABNORMALITIES

  • Chromosomal abnormalities:

    • Occur due to receiving too many or too few chromosomes.

    • Most result from errors in meiosis.

    • Leading cause of pregnancy loss.

  • Examples:

    • Down syndrome: Trisomy of chromosome 21.

    • Turner syndrome: Single X chromosome in females.

    • Klinefelter syndrome: Extra X chromosome(s) in males.

    • Fragile X syndrome: Weak connection on arm of X chromosome.

STUDYING GENETIC AND ENVIRONMENTAL INFLUENCES

  • Behavioral genetics:

    • Studies genetic vs. environmental influences on physical/psychological traits.

  • Heritability:

    • Proportion of trait variability in a sample attributable to genetics.

FAMILY STUDIES: TWINS

  • Twin studies:

    • Compare similarity between identical and fraternal twins to assess genetic influences.

    • Limitations:

      • Generalizability to singleton children.

      • Prenatal environment influence.

      • Treatment similarities affecting psychological outcomes.

FAMILY STUDIES: ADOPTION

  • Adoption studies:

    • Examines psychological similarities between adopted children and their biological/adoptive parents.

    • Limitations:

      • Prenatal environmental effects from biological mothers.

      • May underestimate potential environments children experience.

RESEARCH: ESTIMATING INFLUENCE

  • Concordance rates:

    • Percentage of pairs where one exhibits a trait if the other does.

    • Higher rates imply heritability.

  • Contributions to individual differences:

    • Genes:

    • Shared environmental experiences:

      • Common experiences creating similarities.

    • Nonshared environmental experiences:

      • Unique experiences affecting individuals differently.

THE HERITABILITY OF DIFFERENT TRAITS: INTELLECTUAL ABILITIES

  • Heritability of IQ:

    • Estimated at 0.50, with genetics accounting for 50% of IQ variation.

    • Genetic influence grows with age while shared environmental impacts diminish.

TEMPERAMENT AND PERSONALITY

  • Temperament:

    • Predictable emotional and social responses foundational for personality development.

  • Research indicates living in the same household does not significantly increase personality similarity among children.

THE GENE-ENVIRONMENT INTERPLAY

  • Gene-environment interaction:

    • Genetic influences affect how individuals respond to environments.

    • Psychological disorders may arise from the combination of high-risk genes and adverse environments.

  • Explanations:

    • Diathesis-stress model:

      • Disorders result from genetic vulnerability combined with stress.

    • Differential susceptibility hypothesis:

      • Some genes increase reactivity to environmental influences.

EPIGENETIC EFFECTS ON GENE EXPRESSION

  • Epigenetics:

    • Environmental factors influence gene expression.

    • Explains phenotypic differences in identical twins.

    • Example:

      • Early abuse can lead to heightened stress response systems affecting mental health.

GENE THERAPY

  • Gene therapy:

    • Alteration of a person’s genetic makeup.

    • Applications for disorders like hemophilia and cystic fibrosis have shown success.

    • Ethical issues arise regarding the implications of gene editing.

    • Complexity of most diseases requires consideration of multiple genetic and environmental factors.

CONCLUSION

  • Important topics covered in Chapter 2 – essential to read for further understanding.

  • Reminder of upcoming assignments.

  • Questions encouraged.