biological approach: the relationship between genetics and behaviour Flashcards
gene
- the basic unit of heredity in a living organism
- holds the information to build and maintain their cells and pass genetic traits to offspring
- represents a segment of DNA, is located at a specific point on an organism’s chromosome
genotype
refers to all the genetic information held within the organism’s DNA
phenotype
the expression of the genotype, the observable physical and behavioural traits e.g. hair colour, physique, abilities, hormone levels
→ phenotype is also influenced by environmental factors e.g. geographical location, upbringing, education → this explains why monozygotic twins (identical) don’t have identical personalities/ abilities
alleles
- different versions of the same gene e.g. allele for blue eyes, allele for brown eyes
- Each allele in a pair is inherited directly from each parent
- Alleles create diversity
what is the theory that is preferred over the idea that particular abilities or traits are governed by 1 single gene
seems that people inherit specific vulnerabilities or sensitivities which predispose them to certain conditions e.g. depression
monozygotic twins
- identical
- develop from one fertilised egg which splits and forms two embryos
dizygotic twins
- fraternal
- develop from two different fertilised eggs
concordance rate
the probability that the same trait will be present in both members of a pair of twins
adoption studies
- Researcher investigate similarities between the adoptee and their biological & adoptive parents
- Similarity with biological parent = potentially the result of genetic inheritance
- Similarity with adoptive parent = more likely the result of environmental factors
kinship studies
- Researcher traces a phenotype over several generations in a family tree
- To determine the likelihood that a behaviour is inherited
twin studies
- Researchers compare behavioural traits of MZ and DZ twins
- To evaluate the degree of genetic and environmental influence on a specific trait
- If there is a significantly higher concordance rate among identical twins, the specific trait is likely to be the result of genetic similarity.
- If concordance rates between MZ and DZ twins are similar, the specific trait is likely to be the result of environmental factors.
5-HTT gene
plays a role in serotonin pathways that scientists believe are involved in controlling mood, emotions, aggression, sleep, anxiety
genetic inheritance: a biological theory of depression
- Genetic inheritance is the theory that abnormal behaviour, in this case, depression, can be passed down through genes.
- Diathesis-stress theories of depression predict that an individual’s reaction to stressful events depends on their genetic make-up.
- If an individual has a specific genetic predisposition toward a disorder (genotype), then interaction with stressors in the environment may cause these genes to be expressed
study: Caspi et al (2003) AIM
to investigate the link between the alleles of the 5-HTT gene and depression
study: Caspi et al (2003) PARTICIPANTS + METHOD
- He conducted the study on 847 New Zealand participants aged 26.
- Participants were allocated to groups based on the length of the allele of their 5-HTT genes.
- The groups were: 2 short alleles, 1 short and 1 long allele, or 2 long alleles.
- Participants were evaluated for depression and asked to fill out a questionnaire detailing stressful life events.
study: Caspi et al (2003) RESULTS
- more depression in response to stressful life events was reported from the participants who had the 2 short 5-HTT alleles compared to the other 2 groups.
- the participants with 2 long alleles reported fewer depression symptoms overall.
study: Caspi et al (2003) CONCLUSION
- there may be a relationship between short 5-HTT alleles and depression
- Stressful life events are more likely to trigger depression in people with this genetic makeup.
- Long 5-HTT alleles may provide protection against stress-induced depression
- The onset of depression appears to be an interaction between environment (stressful events) and genetic make-up.
study: Caspi et al (2003) LINK
- Caspi et al.’s (2003) study explains the effect of the 5-HTT on behaviour.
- Participants with 2 short alleles of the gene were most at risk of developing depression after stressful life events compared to those with 2 long alleles.
- Alleles are versions of genes, meaning that genes do affect behaviouR
study: Caspi et al (2003) STRENGTHS
- Researchers exerted control by restricting the measurement of stressful life events in their sample as falling between the ages 21-26 → ensures a degree of consistency across the measurement – increases reliability
- Conducting 3 separate correlational analyses means that each measure is checked by the findings of the other measures → ensures internal validity
study: Caspi et al (2003) WEAKNESSES
- The experience and aetiology of depression is complex and may be due to a number of factors (biological and non-biological) → makes the study reductionist as it provides an overly simplistic explanation
- Using a self-report to collect data is prone to bias (social desirability and response) → reduces the validity of the findings
study: Kendler et al (2006) AIM
to determine the role that genetics plays in major depressive disorder
study: Kendler et al (2006) METHOD
- 42,161 twins, 15,493 complete pairs from the Swedish national twin registry
- Twins were interviewed to determine the level of heritability of depression
- Interviewers assessed lifetime major depression by using modified DSM-IV criteria
- They then evaluated the twin models
study: Kendler et al (2006) RESULTS
- Concordance rates for MDD were significantly higher in women than men
- Correlations were significantly higher in MZ twins than in DZ twins
- No correlation between number of years that the twins had lived together and lifetime MDD
- Estimated heritability of MDD was 0.38, in live with previous research
- No significant differences seen in the roles of genetic and environmental factors in MDD
study: Kendler et al (2006) CONCLUSION
Suggests that the heritability of MDD is higher in woman than in men and that some genetic risk factors for MDD are sex-specific
study: Kendler et al (2006) STRENGTHS
- Confirms previous research, strengthening reliability
- The very large sample size taken from a single population helps to mediate some of the concerns