chapter 2 behavioral genetics

Nature vs. Nurture

  • Nature: Refers to genetic or biological factors, including:

    • Natural genetic makeup

    • DNA structure and expression

  • Nurture: Encompasses environmental factors such as:

    • Family background

    • Neighborhood

    • Educational institutions

    • Societal influences

    • Some consider the womb as part of the environment.

Interaction of Nature and Nurture

  • Nature and nurture interact to shape personality traits and interests.

  • It is not an either/or situation; rather, it is a combination of both influences.

  • Behavioral geneticists study the significance of genetic versus environmental influences on traits like assertiveness and aggressiveness.

Epigenetics

  • A fascinating area that explores how environmental factors can alter gene expression.

  • The course will touch on epigenetics to demonstrate how it plays a role in development.

Behavioral Genetics

  • Definition: Behavioral genetics is the field dedicated to understanding the contributions of genetics and environment on an individual's development.

  • It estimates the extent to which variations among individuals can be ascribed to genetic differences.

  • Concept of Heritability:

    • Refers to the proportion of observable differences in a trait among individuals that can be attributed to genetic differences.

    • Example: Height is influenced by both genes and environmental factors like nutrition.

Case Study: Height

  • Genetic influence on height accounts for 90% of differences in tallness among individuals.

  • Society has observed an increase in average height over the past century attributed to better nutrition rather than genetic mutations.

  • Genes set potential ranges for traits (e.g., height), but environmental factors determine where within that range an individual lands.

Research in Genetics

  • The focus of research studies is often longitudinal, aiming to observe genetic influences over time, including:

    • Changes in phenotype throughout life

    • Genetically influenced conditions like baldness and schizophrenia, which develop later in life.

Gene-Environment Interaction

  • Emphasizes how genetic predispositions influence behaviors based on environmental challenges or experiences.

  • Gene-Environment Correlation:

    • The correlation between genetic predispositions and the experiences one seeks or creates for oneself.

    • Example: Child’s inclination towards reading influenced by parental reading habits.

Key Definitions

  • Genotype: The actual genetic makeup of an organism (e.g., alleles for traits such as eye color).

  • Phenotype: The observable expression of the genotype, influenced by environmental factors.

  • Polygenic Inheritance: Most traits result from the interaction of multiple genes.

  • Incomplete Dominance: When a dominant gene does not entirely express its phenotype (e.g., sickle cell trait).

Sickle Cell Disease

  • Sickle cell disease results from an abnormality in hemoglobin, causing red blood cells to form a banana shape rather than the typical disc shape.

  • Affected individuals may endure a significantly decreased quality of life, with life expectancy typically into the mid-40s to mid-50s.

  • Emphasis on research efforts to improve life quality and outcomes for sickle cell patients, seeking to find effective treatments.

Concordance Rates

  • Definition: A measure comparing the incidence of traits between monozygotic (identical) and dizygotic (fraternal) twins to assess genetic influence.

  • Example of Major Depression:

    • Monozygotic twins' concordance rate: 45.8%

    • Dizygotic twins' concordance rate: 14.8%

  • Findings indicate that the genetic similarity correlates with the likelihood of similarity in traits, affirming genetic influence.

Heritability Estimates

  • Derived from twin and adoption studies; estimates the degree of genetic contribution to traits.

  • For instance, heritability estimate of intelligence is approximately 0.5, suggesting half of the variability in intelligence scores among individuals is due to genetic factors.

  • Important to note that heritability applies to populations, not individuals.

Effects of Environment on Intelligence

  • Gene-environment interactions affect intelligence as determined by the following effects:

    • Passive Genotype-Environment Effects: Parents provide both genetic and environmental factors, complicating the distinction between their influences.

    • Evocative Genotype-Environment Effects: Genetic traits evoke responses from others, shaping one’s experiences (e.g., tall children receiving encouragement to play certain sports).

    • Active Genotype-Environment Effects: Individuals select different environments based on their genetic predispositions (e.g., quieter individuals choosing book reading over socializing).

Summary of Active and Evocative Effects

  • Active: Individual choices reflect genetic tendencies.

  • Evocative: Responses from the environment to genetic traits.

Final Considerations

  • The discussion underscores the importance of understanding the interplay between genetics and environment in psychological development.

  • Encouraged to think of personal examples that illustrate active and evocative effects as preparation for assessments in the course.

Conclusion

  • Thank you for engaging in this module. Looking forward to the next part of our exploration in chapter two!