Genetic factors Flashcards
What is MAO-A (monoamine oxidase A)?
An enzyme that regulates the metabolism of serotonin in the brain.
What is the MAOA gene?
The gene responsible for the activity of the MAO-A enzyme in the brain – the low-activity variant of the gene is closely associated with aggressive behaviour.
Explain the difference between the two types of the MAOA gene
MAOA-L and MAOA-H.
MAOA-L is also named the “warrior” gene and metabolises serotonin at a slower rate than the high activity varient.
Outline a study which reveals the influence of the MAOA gene on aggression.
Brunner et al. (1993) found that males in a Dutch family, who had a history of impulsively aggressive behaviour (rape, attempted murder), had abnormally low levels of MAO-A and the low-activity version of the MAOA gene.
2 Limitations of genetic factors on aggression
Problems with measuring aggression:
Rhee and Waldman (2002) carried out a meta-analysis of adoption studies investigating the genetic influences of aggression. Genetic factors had a greater influence on aggression in studies using self-reports rather than parent or teacher reports. If research findings vary depending upon how aggression is measured, then it becomes very difficult to draw valid conclusions about the role of genetic factors.
Difficult to isolate genetic factors:
Diathesis stress model can provide a more comprehensive explanation - behaviour is only expressed if the environment is favourable.
Caspi et al. (2002) studied 500 male children and found the following results: · Those with the low-activity variant of the MAOA gene (MAOA-L) were significantly more likely to grow up to exhibit anti-social behaviour but only if they had been maltreated as children · Children with the high-activity variant of the MAOA gene (MAOA-H) who were maltreated and those with the MAOA-L variant who were not maltreated, did not display anti-social behaviour. These results suggest a strong gene-environment interaction
Which twin study reveals the influence of genes on aggression? 1 Limitation of this study
Coccaro et al. (1997) found concordance rates of physical assault were 50% for MZ twins and 19% for DZ twins and found concordance rates of verbal aggression were 28% for MZ twins and 7% for DZ twins.
However, in every pair of twins we assume both individuals share the same environment (equal environments assumption). DZ twins may be treated less similarly so concordance rates may be inflated.
1 Strength of genetic factors in aggression (COUNTER)
Research support for MAOA gene:
Brunner et al. (1993)
Mertins et al. (2011) found the converse to be true and that the high-activity variant of the MAOA gene is associated with less aggressive behaviour. They studied participants with the low-activity and high-activity variants of the MAOA gene in a money-distributing game. Found that males with the high-activity variant were more co-operative and made fewer aggressive moves than the low-activity participants.
COUNTER - the study also showed that non- genetic factors play a role. Even participants with the MAOA-L gene behaved co operatively rather than aggressively when they were made aware that other participants were behaving co-operatively. Knowledge of a social norm partly determined how aggressive or co-operative the MAOA-L participants were
Which adoption study reveals the influence of genes in aggression?
Hutchings and Mednick (1975) found that a significant number of adopted boys in Denmark with criminal convictions had biological parents with convictions for criminal violence also.
