Top 10 Replicated Findings from Behavioural Genetics.pdf

Top 10 Replicated Findings from Behavioural Genetics 11 December 2023 15:03 Main Ideas Notes Top 10 replicated findings from behavioral genetics. Perspectives on psychological science (Plomin et al., 2016) ○ Context: this study was published amidst the replication crisis in psychological science ○ T...

Top 10 Replicated Findings from Behavioural Genetics 11 December 2023 15:03 Main Ideas Notes Top 10 replicated findings from behavioral genetics. Perspectives on psychological science (Plomin et al., 2016) ○ Context: this study was published amidst the replication crisis in psychological science ○ Ten ‘big’ finding: in terms of effect size and impact on psychological science, that have robustly replicated. ○ Include discoveries about the environment that could only have been found using genetic designs. ○ Findings are not novel but repeatedly verified ○ 'Findings’, rather than ‘laws’: ▪ Exceptions ▪ Limited to samples, measures, and methods ▪ Most (but not all) supported by meta-analyses ▪ Most behavioral geneticists will agree, but most would also wish to add to the list ▪ Most findings supported by meta-analysis Finding 1: All psychological traits show significant and substantial genetic influence ○ Data from McGuffin et al. (2001) Notes Finding 2: No complex traits are 100% heritable ○ Heritability (h2) estimates are significantly less than 100% ○ Not due to limitations of methods (measurement error) ○ Some physical and physiological traits show h2 > 90% ○ Strongest evidence for the importance of environmental influence can be gained after controlling for genetic influence Notes Finding 6: Age-to-age stability is largely due to genetics (Bivariate heritability) ○ Supported for: personality, intelligence, psychopathology ○ Intelligence: What explains genetic stability despite increasing heritability? ▪ Genetic “amplification” via selective gene-environment correlation ▪ ○ This graph shows that psychological traits are substantial ○ Finding 7: Most measures of the environment show significant genetic influence Finding 3: Heritability is caused by many genes of small effect ○ DNA-based methods support basic quantitative genetic model (Fisher, 1918) ○ GWA: ▪ largest effect sizes are extremely small ○ Great power is needed to detect small effects: ▪ There are no large effects in the population. ○ Implies that h2 caused by many genes of small effect. ○ Genome-wide Complex Trait Analysis (GCTA): ▪ SNPs on all chromosomes contribute to h2 ○ Example: Parental control/ Warmth & Adolescent substance use (Plomin & Bergeman, 1991) ○ Purple graphs show heritability rates and top bar graphs are twin correlations (Polderman et al., 2015) Finding 8: Most associat Finding 4: Phenotypic correlations between behavioral traits show significant and substantial genetic mediation (Bivariate heritability) ○ Example: cognitive abilities and disabilities ▪ Over half of phenotypic correlations among cognitive abilities and disabilities can be attributed to genetics ▪ Supported by GCTA □ Studies: Plomin & Kovas (2005) □ Trzaskowski et al. (2013) ○ Example: Psychopathology ▪ Phenotypic co-morbidity across common disorders is largely driven by genetics ▪ Supported by GCTA and GWAS ▪ Example by Kavanagh et al (2015): “Schizophrenia has substantial overlaps with bipolar disorder, intellectual disability, major depressive disorder and autism spectrum disorders ○ More than 100 stu ▪ Family envir ▪ Family envir ▪ Family envir ▪ Social suppo ▪ SES and IQ ▪ SES and aca ▪ Peer devian ○ GCTA replication ▪ SES vs. IQ (a Finding 9: Most environ ○ Quantitative gene ○ Genetics accounts ○ The environment ○ Likely that nonsha ○ Example: graph fr ▪ ▪ ○ Example: quantity/quality of social support and loneliness Finding 10: Abnormal is ○ Common disorder Finding 5: Heritability of intelligence increases throughout development ○ Graph from Plomin (1986) ▪ ○ Graph from Haworth et al. (2009) ○ Convergence across family, twin and adoption studies ○ No exceptions (yet?) ▪ To disprove it: Reliably measure a trait, in an adequately powered study, and find non-significant heritability ○ Not just significant but also substantial genetic influence ▪ ~30-50% heritabilities ○ Estimates from DNA alone generally support conclusion ▪ ○ GWA studies prov ▪ Genes assoc ○ “We all carry som ○ Example: Graph (T continuous traits ▪ Summary 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. All psychological traits show significant and substantial genetic influence No complex traits are 100% heritable Heritability is caused by many genes of small effect Phenotypic correlations between behavioral traits show significant and substantial genetic mediation The heritability of intelligence increases throughout development Age-to-age stability is largely due to genetics Most measures of the environment show significant genetic influence Most associations between environmental measures and psychological outcomes are significantly mediated genetically Most environmental effects are not shared by children growing up in the same family Abnormal is normal PSYC0036 Genes and Behaviour Page 1 ations between the environmental measures and behavioural traits are significantly mediated by genes udies showed consistent results: ronment and IQ ronment and psychopathology ronment and personality ort and depression demic achievement ce and conduct disorder and educational achievement) nmental effects are not shared by children growing up in the same family etic designs can separate nature from nurture in family resemblance s for nearly all family resemblance is important, but its most salient aspects are those that contribute to individual differences (vs. family re semblance) ared environmental effects are due to many experiences of small effect rom McGuffin et al. (2001) s normal rs are quantitative extremes of the same genetic & environmental factors responsible for normal variation vided strong evidence: ciated with disorders (case-control) are also associated with dimensions (quantitative traits) & vice versa e degree of risk” (Kendler, 2015, Molecular Psychiatry) Taylor et al., 2017) - Genetic and nonshared environmental correlations between psychiatric diagnoses and from the best-fitting twin models PSYC0036 Genes and Behaviour Page 2 PSYC0036 Genes and Behaviour Page 3 PSYC0036 Genes and Behaviour Page 4