2g. Genes and behaviour Flashcards
Nature vs Nurture debate
Establishes whether human behaviour is determined primarily by biological factors or environmental
Diathesis-stress model
Predicts that an individual with certain genes, when exposed to a stressful environment, is more likely to develop depression than someone who doesn’t have those genes
What argument does diathesis-stress model support?
Argument that a person may have a genetic predisposition towards a behavior, however without appropriate environmental stimuli, gene is not “activated” and hence will not be expressed
Indirect methods of genetic research
- Kinship/family studies
- Twin studies
- Adoption studies
Direct methods of genetic research
- Linkage studies
2. Genome wide association studies
Monozygotic twins
Those who develop from same egg and share 100% genotype
Dizygotic twins
Develop from different eggs and share 50% genotype, like regular siblings
Concordance rate
Probability that same trait will be present and expressed in both twins. Rarely ever 100%
Principle of genetic relatedness
The higher the genetic similarity between two individuals, the more likely it is for a particular characteristic to be present in both individuals
Why are twin studies used?
- Identical twins allow us to study effect of genetics
- Fraternal allow us to see the effect of environment as they have different DNA
Limitations of twin studies
- Twins are rarely raised apart so they experience similar environment hence difficult to isolate environmental influence as a variable
- Equal environment fallacy
- Twins are not highly representative of general population- less generalizability
- Concordance rate is rarely 100% so genetics can never be implied as direct causation
Equal environment fallacy
Assuming that twins grow in equal environment. We have to be careful not to overestimate the similarity of environment
Family studies
Look at concordance rate within a family, usually over 3 generations
Why are family studies used?
- Sample is more representative of general population
- Allows for similarity in culture and environment
Limitations of family studies
- Members share same environment
- No actual gene identification
- Anecdotal/ self-reported data
- Waiting for generations is an inefficient strategy
Adoption study
Comparing adopted children to their biological and adopted parents and biological/adopted siblings to determine higher concordance rates
Why use adoption studies?
- Easier to infer exact influence of genetics
- Allow researcher to more directly investigate role of environment and genetics
- Research can isolate variables
Limitations of adoption studies
- Children are not representative of the general population
- Adoption tend to use selective placement when finding homes
Which twin study can be used for depression?
Kendler et al. (2006)
Kendler: Aim
To investigate the role of genetics in depression
Kendler: Procedure
- Carried out twin study of over 20000 twin pairs in Swedish national twin registry
- Studied monozygotic and dizygotic twins
- Researchers used a team of interviewers to carry out telephone interviews
- They assessed lifetime major depression by using modified DSM-IV criteria
- Questions were also asked regarding the environment they lived in
Kendler: Results
- Over 8000 twins met criteria for depression while around 300 discussed discussed history of anti-depressant treatment
- Found avg. CR for MZ male twins was 31% while for MZ female twins was 44%
- 11% and 16% for DZ male and female twins
- Genetic risk factors may be sex-specific
- No correlation between no. of years in shared environment and depression
- CR is way below 100% so genetics is not cause but rather a vulnerability
Kendler: Evaluation
- Studies are correlational
- No specific genes identified
- Other twin studies have had similar results so its reliable
- All data was self-reported
- Investigators relied on previously accepted diagnoses
- Sample size was large
Family study for depression
Weissman et al. (2005)
Weissman: Aim
Study the potential genetic nature of MDD
Weissman: Procedure
- Took place over 20 year period
- Sample of 160 grandchildren and their families
- Original sample of depressed patients (grandparents) was selected from specialized clinic. Non-depressed patients were also selected
- All 3 generations were interviewed many times and data was collected by clinicians blind to past diagnosis of depression
- Researcher triangulation was used to establish credibility of diagnosis. Used psychiatrist and psychologist
Weissman: Results
- High rates of psychiatric disorder in grandchildren with two generations of depression
- Less risk if it wasn’t observed in second generation
- Severity of parent’s depression was correlated with increased rate of mood disorder in children
- If parent was depressed but no history in grandparent, no significant effect on grandchild
Weissman: Evaluation
- Study is longitudinal so reliable
- Association between parent and child is moderated by grandparent
- Use of research triangulation
- Sample is large but not many replications
- No genotype is studies but it indicates potential genetic link
- 3 generations is limited however to go further back, one is reliant on memory and anecdotal data= distortions
