Genetics as an explanation for behaviour

Question 1

Define the gene environment interaction

Answer 1

behaviour is the interaction of genetic inheritance and environmental factors
Diathesis stress model:
-behaviour is a predispositional genetic vulnerability expressed as a result of stress from life experiences
- gene is a switch, environment switches it on

Question 2

define depression

Answer 2

a mood disorder characterised by low mood and disinterest in things that used to give pleasure for a person, diagnosed by the DSM-5

Question 3

define the 5-HTT gene

Answer 3

Responsible for the coding of transporter proteins in axon terminals specific to the re-uptake of serotonin after an action potential.
- number of serotonin transporters determines the length of time that serotonin will stay in the synaptic cleft before re-uptake

The 5-HTT gene has 2 alleles ‘s’ (mutated) and a ‘l’ version
- s version produces less serotonin transporter proteins than the l version.

Those with an allele combination including at least one ‘s’ allele have the higher rates of depression than those with two ‘l’ alleles
- ss is highest

Question 4

Caspi et al

Answer 4

Aim: To investigate whether a functional change in the 5HTT gene is linked to a higher or lower risk of depression in an individual

• longer periods of time spent in synaptic cleft —> more degredation of serotonin
  
  • serotonin is linked to *mood and concentration
• quasi-experiment
• longitudinal experiment

Participants: 847 26-year olds from New Zealand

Procedure

1. The participants were split into 3 groups based on their 5-HTT alleles
   
   • ss, sl, and ll
2. Stressful life events occurring after the 21stbirthday and before the 26thbirthday were assessed using a life-history calendar.
3. Past-year depression was assessed using the Diagnostic Interview Schedule.
4. A correlation was tested for between stressful life events and depression, and also between the length of the alleles and depression, as well as interaction between perceived stress and the length of the alleles.
5. A further test was done to see if life events could predict an increase in depression over time among individuals with one or two short alleles.

Results

• Childhood maltreatment was predictive of depression in adulthood only in adults with one or more s alleles
• Researchers found that participants with one or more short alleles were genetically vunerable/predisposition to depression. Two long alleles served as a protective factor against depression

Conclusion
Researchers concluded that there is a relationship between short alleles and incidences of stress and subsequent depression, and that the effects of gene adaptation are dependent on environmental exposure to stress

Evaluation

• very large cohort of participants
• ethnocentricity
• age was controlled to isolate the variable of number of stressful life events
• actions of other genes could not be controlled, reductionist
• assumption that serotonin causes depression
• life events were catagorised quantify the measure
• symptoms were self reported, even though a colleague was contacted, can still be inaccurate
  
  • underreporting due to stigma - dishonesty
  • participant bias
  • possible a colleague doesn’t know wellbeing status