Genetic explanations

I have always been bothered by the fact that it is considered legitimate to answer exam questions on genetic explanations by describing research studies – surely it must be possible to actually explain how genes might cause, for example aggression or schizophrenia?

I presented two descriptive passages to AQA to see what they thought of my attempts. One was a genetic explanation of aggression and one was a genetic explanation of schizophrenia. Both were about 200 words and were judged to be worthy of top band marks. So it can be done and means research studies can be used as AO2.

Here are my examples:

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Describe one biological explanation of aggression:

Aggressive behaviour can be explained in terms of genetics. What this means is that and individual inherits genes that lead to the disorder. It would certainly not be one gene because only very simple characteristics are caused by one gene and aggression is complex.

Although no individual gene for aggression has been identified in humans, a gene responsible for producing a protein called monoamine oxidase A (MAOA) has been associated with aggressive behaviour. MAOA regulates the metabolism of serotonin in the brain, and low levels of serotonin are associated with impulsive and aggressive behaviour.

In the case of men the suggestion is that their genetics leads to the production of testosterone in higher levels than in females and this hormone creates higher levels f aggression. Such behaviour has evolved because men are hunters and protectors and therefore it is important for them to respond in certain situations with aggressiveness.

In the case of people who commit violent crimes researchers do not suggest that there is a gene for violent crime per se. Rather it is claimed that inherited temperamental or personality characteristics place some individuals more at risk of committing violent crime. Adoption studies have shown that the highest rates of criminal violence in adopted children occur when both biological and adoptive parents have a history of violent crime – clear evidence of a gene-environment interaction.

Examiner comments: The description of genetic factors in aggression is exemplary, even if the link between genes, evolution and testosterone/aggression in men could perhaps have been a fraction clearer. Marks awarded in any sitting of the examination are dependent on decisions made at the standardization meetings, but this would certainly be in the top band and arguably maximum AO1 marks.

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Describe one biological explanation of schizophrenia

Schizophrenia can be explained in terms of genetics. What this means is that an individual inherits genes that lead to the disorder. It would certainly not be one gene as this is a complex disorder with a range of different characteristics (e.g. not all patients experience delusions). The explanation is also one of diathesis-stress, that is that individuals may possess certain candidate genes but the likelihood that the genes are actually expressed as schizophrenia depends on ‘stressors’.

One of the possibilities is that such genes lead to overproduction of dopamine. Individuals inherit abnormally high numbers of D2 receptors on receiving neurons. The consequence is that the dopamine neurons fire too easily and/or too often and this results in higher levels of dopamine than normal at synapses. Dopamine neurons play a key role in guiding attention, so disturbances in this process may well lead to the problems relating to attention, perception and thought found in people with schizophrenia (Comer, 2003).

The genetic explanation includes the element of diathesis. It does not propose that the disorder is solely caused by genes. One current suggestion is that overuse of strong cannabis may act as a trigger in vulnerable individuals. Other alternative suggests have been traumatic childhood experiences.

Examiner comments: If the question asked for one biological explanation of schizophrenia, your information would be sufficient for top band marks. If the question asked for 2 biological explanations of SZ,  the coverage of dopamine is accurate and detailed and the answer makes a notable effort to link biological explanations together – which should be rewarded. However, coverage of genetics is not well detailed: mark schemes for PSYA4 acknowledge the difficulties in describing genetic explanations and credit can be awarded for straight descriptions of  studies which demonstrate heritability –  this could also be included here as could material on more recent gene discoveries (PCM1 etc).

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