With reference to relevant research studies, discuss the extent to which genetic inheritance influences human behaviour

Question 1

What is gene mapping? (2)

Answer 1

• the attempt to determine the effect of a particular gene
• on behaviour such as psychological trains (temperament), psychological disorders (e.g. depression of schizophrenia) or various psychological conditions

Question 2

Name a relevant study to gene mapping (1)

Answer 2

Caspi et al. (2003) Longitudinal study on the possible role of the 5-HTT gene in depression after experiences of stressful events

Question 3

Outline Caspi et al. (2003) Longitudinal study on the possible role of the 5-HTT gene in depression after experiences of stressful events (5)

Answer 3

• 5-HTT gene influences the level of serotonin = known to play a role in controlling mood
• researchers compared participant siwht normal 5-HTT gene and mutation of 5-HTT gene with shorter alleles
• both genes quite common but longer allele is more frequent - 57%
• researchers found that mutation of 5-HTT gene + experience of many stressful events = more likely to become depressed after stressful events compared to normal 5-HTT gene carriers
• 5-HTT gene could indicate a vulnerability to depression after stress + researchers speculated whether the gene could moderate individual responses to environmental factors

Question 4

Evaluation of Caspi et al. (2003) Longitudinal study on the possible role of the 5-HTT gene in depression after experiences of stressful events (5)

Answer 4

• since 43% of pop carry mutation + they don’t all have depression = can be difficult to conclude 5-HTT has a major contribution to depression
• people who do not carry mutation also became depressed
• study showed correlation between mutated 5-HTT and depression but impossible to establish cause-effect
• genes contribute but unclear how environmental factors influence behavioural traits = no evidence against the idea that it could just be the stressful events that made people depressed
• much more research is needed before a clear relationship between a gene and a behavioural trait can be established

Question 5

Where do MZ twins come from? What % of their genes do they share? Where do DZ twins come from? What % of their genes do they share? % of their genes do siblings share? (5)

Answer 5

• same egg
• 100%
• two different eggs
• 50%
• 50%

Question 6

What is concordance rate? What is it assumed to establish? (2)

Answer 6

• likelihood or probability that if one individual has the trait the other will also have it
• to what extent a certain trait is inherited

Question 7

What is useful about twin studies? What did the classic twin study study? What can be assumed when MZ twins are raised separately? (3)

Answer 7

• one twin acts as a control for the other twin
• concordance rates and did not include environmental factors
• assumed that differences were due to environmental factors

Question 8

Why are sets of MZ compared to sets of DZ for a particular trait/ disorder? What are differences between MZ twins attributed to? (2)

Answer 8

• high concordance rates in MZ twins and lower concordance rates in DZ twins for same behaviour = that trait/ disease is linked to genes (inherited)
• environmental factors

Question 9

Name a study relevant to twin studies. (1)

Answer 9

• Bouchard et al. (1990) Twin study investigating genetic inheritance in intelligence

Question 10

Outline Bouchard et al. (1990) Twin study investigating genetic inheritance in intelligence (6)

Answer 10

• self-selected sample of MZ twins who had been reared together (MZT) and MZ twins who had been reared apart (MZA)
• to investigate concordance rates for a number of variables such as IQ
• results showed that for IQ (measured by standardized intelligence test called WAIS) the concordance rate was 69% for MZA and 88% for MZT
• researchers concluded that environmental factors do play a role in development of intelligence but IQ is to a large extent inherited + that 70% of the observed variation in the sample = attributed to genetic variation
• calim that results indicate that in sample like the one in study (white, middle-class in industrialised nation) genetic inheritance in IQ accounts for around two-thirds of observed variance of IQ
• also said that findings do not indicate that IQ cannot be increased, that is influence by environmental factors

Question 11

Evaluation Bouchard et al. (1990) Twin study investigating genetic inheritance in intelligence (5)

Answer 11

• correlational data =/= establish cause-effect relationship
• concordance rates = high but far from 100% = difficult to determine the relative influence of genes
• calculation of concordance rates not always reliable
• no control for effect of environmental variables in study = affects accurate estimations of genetic contribution to intelligence
• findings from self-selected sample = difficult to generalise findings

Question 12

Problems in genetic research (4)

Answer 12

• Genetic research cannot at this point determining the extent to which genetic inheritance influence behaviour because:
• genes interact with environmental factors in complex ways = difficult to measure relative influence of genes and environmental factors
• knowledge about genes = limited
• problems in genetic research: MZ twins being treated in the same way as DZ twins may be wrong (“equal environment assumption” = flawed) = limits possibility of drawing meaningful conclusions from twin studies

Question 13

With reference to relevant research studies, discuss the extent to which genetic inheritance influences human behaviour

Answer 13

Gene mapping definition
Caspi et al. (2003)
Twin studies 
Bouchard et al. (1990)
Problems in genetic research