Genetic similarity Notes

Methods of Study

Twin Studies

1. Twin studies are fundamental to understanding the genetic basis of behavior. There are two types of twins:
   1. Monozygotic (MZ) Twins: Identical twins who share 100% of their DNA.
   2. Dizygotic (DZ) Twins: Fraternal twins who share approximately 50% of their DNA, similar to regular siblings.
2. By comparing MZ and DZ twins, researchers infer the extent of genetic influence on specific traits.
3. Greater similarity in MZ twins compared to DZ twins suggests a stronger genetic component.
4. Results are often given as a concordance rate, which ranges between 0 (no similarity) and 1 (perfect similarity)

Adoption Studies

1. Adoption studies separate genetic and environmental influences by studying individuals raised apart from biological relatives.
2. Comparisons between adopted children and their biological and adoptive families help identify contributions of genes and upbringing.

Family Studies

1. Examine behavior across several generations, exploring how traits are passed down.
2. Include a broader genetic spectrum, such as siblings, cousins, parents, and grandparents.

Molecular Genetics

• This approach identifies specific genes associated with behaviors through genetic mapping and epigenetic studies.
• Explains how certain genes are expressed or suppressed in response to environmental factors.

Key Studies

Twin Study on Antisocial Behavior

Adoption Study on Antisocial Behavior

Meta-Analysis of Twin and Adoption Studies

Twin Study on Intelligence

The 5-HTT Gene and Stress

Critical Thinking

Triangulation for Robust Findings

1. All methods may carry observer biases or cultural influences.
2. Using multiple sources of data, such as self-reports, caregiver questionnaires, and teacher assessments (Baker et al., 2007), strengthens the validity and reliability of findings.
3. Triangulation minimizes biases inherent in any single method.

Dynamic Interactions Between Genes and Environment

1. Niche-Picking: Genetic predispositions may lead individuals to actively shape their environments.
2. Epigenetics: Environmental factors, such as stress or nurturing, can regulate gene expression.

Methodological Limitations

1. Assumptions in Twin Studies:
   1. The equal environments assumption posits that MZ and DZ twins experience similar environments apart from their genetic differences.
   2. However, MZ twins may be treated more similarly than DZ twins, potentially inflating heritability estimates.
   3. Small sample sizes in twin studies limit generalizability, especially for rare behaviors or traits.
2. Challenges in Adoption Studies:
   1. Assume that biological parents provide only genetic influences and adoptive parents provide only environmental influences.
   2. Prenatal factors or selective adoption practices (e.g., adoptees placed in families similar to biological ones) can confound findings.
   3. Limited availability of participants reduces diversity and generalizability.
   4. Researchers cannot separate children from their family, as it would be unethical so they must find participants who were adopted, which is difficult.
3. Correlation vs. Causation:
   1. Genetic studies often reveal correlations but cannot establish causation.
   2. A high heritability score (Baker et al., 2007) indicates a genetic contribution but does not pinpoint specific causal mechanisms.

Variability in Heritability Estimates

1. Heritability estimates, such as the 50% found for antisocial behavior (Baker et al., 2007), are population-specific and not universal constants.
2. The same behavior may have varying heritability at different life stages.
   1. Grove et al. (1990) found antisocial behavior had a higher genetic influence in childhood (41%) than in adulthood (28%), suggesting the environment’s growing impact over time.

Ethical Considerations

1. Privacy and Stigmatization:
   1. Genetic findings could be misused to label or stigmatize individuals or groups.
   2. For example, associating certain genes with antisocial behavior could lead to discrimination.
2. Informed Consent: Participants must fully understand the implications of genetic research, especially in studies involving genetic mapping.
3. Genetic Determinism: Overemphasis on genetics risks promoting the false belief that behaviors are entirely predetermined, undermining the role of environmental interventions.

Broader Implications

1. Cultural Bias: Many twin and adoption studies are conducted in Western contexts, where cultural norms and socioeconomic factors may differ significantly from other regions.
2. Policy and Interventions: Understanding the interaction between genes and environment can inform policies targeting environmental factors, such as improving access to education or reducing socio-economic disparities.