Salters-Nuffield Advanced Biology Resources Activity 3.18 Teacher Sheet

GENES OR THE ENVIRONMENT

Purpose

 To appreciate the difficulty of determining the extent to which characteristics in organisms are caused by genetic or environmental factors.

This activity uses a case study to explore the effect of genes and the environment on behaviour characteristics in humans. It considers research evidence for an interaction between the genetics of monoamine oxidase A (MAOA), childhood maltreatment and antisocial behaviour.

There are video clips that could be used to introduce the activity. Some nickname the MAOA gene as ‘the warrior gene’.

Answers

Q1 A longitudinal study is similar to a cohort study, when the same group of individuals is followed over a long period of time. The Dunedin study enables researchers to build up as full a picture as possible of the influences affecting the individuals. It is not looking at the

development of a disease. Examples of longitudinal studies on humans include those upon which the television series ‘7 Up’ and ‘Child of our Time’ are based, and the Avon

Longitudinal Study of Parents and their Children (ALSPAC) or ‘Children of the ’90s’ study at the University of Bristol.

A classic longitudinal animal study is the Isle of Rum red deer research project, undertaken by the Universities of Cambridge and Edinburgh.

Q2 Males of Maori descent were excluded from the King’s College analysis to eliminate variations due to ethnic origin.

Q3 Neurotransmitters are chemicals that allow information from nerve impulses to be carried across the gaps or synapses between nerve cells and then initiate nerve impulses in the next nerve cell. Monoamine oxidase A is an enzyme that removes neurotransmitters from the synapse after the transmitter has carried out its function.

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Q4

a Normal MAOA levels b Low MAOA levels

Students should have come across synapses and neurotransmitters at GCSE, but terms like vesicles, receptors, pre- and post-synaptic neurones, and action potentials are unlikely to be known. Annotations are likely to be fairly simple.

Q5 Males have only one X chromosome whilst females have two. A male with XM _{Y genotype} will have normal high levels of MAOA, but a male with Xm _{Y will have low levels. Males} must inherit their X chromosome from their mother. A woman would need to have Xm _Xm genotype to be affected by low MAOA levels. Either of the other two female genotypes, XM _Xm _{or X}M _XM _{would be normal.}

Q6 The MAOA ‘knock out’ mice do not produce the enzyme monoamine oxidase A, because the gene for this has been deleted. MAOA removes neurotransmitter molecules from synapses. Therefore without MAOA these ‘knock out’ mice will have high levels of neurotransmitter in their synapses compared with normal mice.

Q7 Researchers have to observe normal mice and record how normal mice react to different situations. They can then compare the behaviour of the ‘knock out’ mice. The researchers would have to agree what constitutes fearless and aggressive behaviour in mice in advance of the study to ensure the results are valid.

Q8 Confirmation of the findings of the Dunedin study by others enhances the reliability of the study’s findings.

Q9 Dutch study found:

MAOA deficiency in aggressive males. Dunedin study found:

Low MAOA + maltreatment  higher antisocial behaviour High MAOA + maltreatment  lower antisocial behaviour Low MAOA + no maltreatment  lower antisocial behaviour

No, we cannot conclude that antisocial behaviour is caused by a genetic mutation, as

maltreatment must also occur. The study indicates a correlation, not necessarily causation. The article gives no clear mechanism to explain how maltreatment as a child results in antisocial behaviour. Both the genetic factor (the mutant MAOA gene) and an environmental factor (maltreatment in childhood) have to be present – and even then 15% of the individuals still did not exhibit antisocial behaviour, even when both of these factors were present.

Neurotransmitter remains, not broken down, so impulses continue to occur in second nerve cell MAOA enzyme removes

neurotransmitter No further impulses in second nerve cell

Electrical impulses in first nerve cell Neurotransmitter released

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Q10 Students may come up with different explanations. For example, an environment with maltreatment of a child may cause methylation of the MAOA gene so there is reduced expression of the gene. In children with the mutation that causes low levels of MAOA, methylation may mean very little production of MAOA, which leads to aggressive behaviour. In children with no maltreatment the gene is not changed epigenetically and it is expressed, thus the low levels of MAOA produced may be sufficient to prevent antisocial behaviour. It has been hypothesised that changes in the MAOA balance caused by severe environmental factors could alter MAOA-mediated brain development, influencing neural pathways associated with emotions.

Q11 Examples of the social, moral and ethical issues these reports raise could include:

 Is it in the interest of society to test vulnerable individuals?

 Is it in the interest of the individual to be tested?

 Whose rights are paramount – those of the individual or those suffering the effects of the antisocial behaviour?

 What restrictions should be placed on the use of such a test?

 Who should have access to the test results?

 Will children testing positive be ‘labelled’?

 Will testing result in a self-fulfilling prophecy?

 Should all children with antisocial behaviour be tested?

 How will the results of the test be used?

 What long-term side-effects might the corrective drug treatment have?

 What happens if the drug treatment is ineffective for an individual?

 What if the drug is expensive and the health authority cannot afford it?

 What happens if the child is too old for the drug to have any effect?

 Should an individual with the mutant MAOA gene and a history of childhood abuse be responsible for their criminal actions in a court of law? (‘It wasn’t me, it was my genes!’)

 Would knowledge of a person having the mutant gene bias the legal system in cases of antisocial behaviour?