Lecture 2 - Heritability (PDF)

# Lecture 2 ## 10/15 Will ### Francis Galton (1869) "Hereditary Genius" - Found similarities in IQ transfer through generations and genetics. ### How to prove this: - Twins - Family resemblance & study the differences - Adoption ### Major Assumption: - Traits affected by genetics show up in s...

# Lecture 2 ## 10/15 Will ### Francis Galton (1869) "Hereditary Genius" - Found similarities in IQ transfer through generations and genetics. ### How to prove this: - Twins - Family resemblance & study the differences - Adoption ### Major Assumption: - Traits affected by genetics show up in similar individuals. _Problems with this_ - Environment impacts genetics. - Need designs to disentangle genes and environment. ### Adoption & Twin Studies: 1. Genetically similar people raised in different environments. 2. Genetically unrelated people in the same environment. ### Monozygotic Twins: - Share 100% DNA ### Dizygotic Twins: - Share 50% DNA ### 3 Sources of Variability in Twin Studies: 1. Genes 2. Shared Environment 3. Non-Shared Environment ## Heritability (H) - The proportion of total variation of a given characteristic in a population that can be attributed to genetic differences between members of the population. - Variation not attributable to genes is caused by differences in environment. $H = \frac{G_u/P_u}{}$ - Always between 0 and 1. ### Phenotype (Observed Data) - Expression of genetic factors (Gu) influenced by environment. ### Genotype (Latent Causes) - Genetics (Gu) ### H depends on: - Genetic variability of a population. - Degree of variability in environment. ### H is NOT absolute! ## Problems with H Estimates: 1. Genotype-environment correlations & interaction 2. IQ ratios vary with socioeconomic status. 3. Age comparison (It can change based on what age people are) 4. Selective placement of adoption. _Remember, H is a population statistic, not an individual one._