Sample response

As a result of the Human Genome Project, psychologists have moved beyond simple twin studies and now can look at the role of a specific gene in a behaviour.  Often look at how different genetic mutations may play a role in a behaviour.  Caspi et al (2003) examined the role of the 5-HTT gene in depression, a gene known as a "serotonin transporter" gene, it regulates the level of serotonin in the synapse. Psychologists believe that serotonin plays a role in mood and therefore plays a role in human depression. The long allele is the "normal" allele; the short allele is the mutation. Caspi wanted to test if people who inherit two short versions of the 5-HTT gene are more likely to develop major depression after a stressful life event than people with two long alleles.

Caspi used a sample of over 800 New Zealand 26-year-olds. The study was a correlational study. Participants were divided into three groups: Group 1 had two short alleles; Group 2 had one short and one long allele; Group 3 had two long alleles. The participants were asked to fill in a "Stressful life events" questionnaire.  They were also assessed for depression.

People who had the two short versions of the allele and had three or more stressful life events were the most likely to have depression. Simply inheriting the gene was not enough to lead to depression, but the genes' interaction with stressful life events increased one's likelihood of developing depression. It appears that by inheriting the mutation of the 5 HTT serotonin transporter gene, one is more vulnerable to the disorder.

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