Week 6

Question 1

Family and Adoption Studies

Question 2

What is heritability?

Answer 2

• Proportion of differences in a population that can be explained by genetics
• Personality is heritable

Question 3

What is a heritability estimate?

Answer 3

• The proportion of variation in a population trait that can be attributed to inherited genetic factors
• A number between 0 and 1, like a correlation

Question 4

Candidate Gene Approach (CGA)

Answer 4

• Involves assessing the association between a particular allele (or set of alleles) of a gene that may be involved in the disease (i.e., a candidate gene) and the disease itself
• Start with a candidate gene in mind
• Constrained by prior knowledge
• Allows systematic scanning

Question 5

CGA and the problem of non-replication

Answer 5

• There have been reports of association between genes and personality traits
• Evidence is strongest for HTTLPR (neuroticism) and some indications for DRD4 (extraversion)
• However, the effects are small and may also vary with sex and ethnicity
• You would need thousands of participants to reliably detect associations
• Even if they are real, they don’t explain much of the genetic basis of personality

Question 6

Genome-Wide Association Studies (GWAS)

Answer 6

• Set markers across the whole genome
  -Should find all variants associated with phenotype of interest
• Hypothesis-free
• Exploratory
• Lower power
• Large number of variants

Question 7

GWAS and the problem of the missing heritability

Answer 7

• For personality, each GWAS finds some associations but these initially explain <1% of the variance and usually did not replicate across studies
• Problem is we may have overestimated heritability
• There are multiple genes that all have a small effect (massive polygenicity)

Question 8

Epigenome/Epigenetic Factors

Answer 8

• Epigenome is a secondary layer of biochemical information that modify or mark the genome in a way that alters the instructions given by the DNA
• Epigenetic factors impact on DNA and gene activation (influence which genes are turned on and off at different times and places in the body)
• While the genome remains largely static within an individual, the epigenome can be altered by the environment
• Epigenetic changes can be passed down generations by transgenerational epigenetic inheritance

Question 9

GxG and GxE Interactions