Genetic Explanations of Offending | AQA A-Level Psychology Revision

Revision Notes
Aug 7
28 min read

Updated: Aug 14

For 7182 specification, first teach in September 2025

AQA A-Level Psychology | Free Revision Notes

Estimated study time: 65 to 80 minutes

Genetic explanations of offending A-Level Psychology revision examines whether inherited biological differences can increase a person’s vulnerability to offending behaviour. You will learn how family, twin and adoption evidence may be used to investigate inheritance, how the MAOA gene may influence impulsive or aggressive behaviour and why genes should be viewed as risk factors rather than direct causes of crime.

This lesson begins the biological explanations of offending required for Forensic Psychology. It prepares you for brain functioning and offending behaviour [Lesson 5: Neural explanations of offending], where the biological processes through which genetic vulnerability may operate are considered in greater detail.

The current AQA specification requires genetic and neural explanations as the two biological explanations of offending behaviour.

Learning Objectives 🎯

By the end of this revision page, you should be able to:

Define genetic vulnerability, genotype, phenotype and heritability.
Explain how inherited characteristics may increase the likelihood of offending.
Explain how family, twin and adoption studies investigate genetic influence.
Explain the possible role of the MAOA gene.
Apply genetic vulnerability to unfamiliar examples of offending.
Distinguish genetic predisposition from genetic determinism.
Evaluate genetic explanations using evidence, methodological issues and wider debates.

Revision Notes 📚

Genetic Explanations of Offending A-Level Psychology Revision Focus

A genetic explanation proposes that inherited biological differences contribute to the likelihood of offending behaviour.

Genes may influence characteristics associated with offending, such as:

Impulsivity.
Aggressive responding.
Emotional regulation.
Sensitivity to rewards and punishment.
Self-control.
Responses to stress.
Vulnerability to antisocial behaviour.

The explanation does not need to claim that someone inherits a particular offence.

A person does not inherit:

Burglary.
Fraud.
Assault.
Theft.
Vandalism.

Instead, they may inherit characteristics that make certain behaviours more likely under particular environmental conditions.

The basic proposal is:

Genetic vulnerability → biological or behavioural predisposition → interaction with environmental experience → increased likelihood of offending

Genes and DNA

A gene is a section of deoxyribonucleic acid, usually shortened to DNA.

Genes provide instructions involved in:

Producing proteins and enzymes.
Brain development.
Neurotransmitter regulation.
Hormonal processes.
Physical and psychological characteristics.

People inherit genetic material from both biological parents.

This means that biological relatives share a proportion of their genes:

Identical twins share effectively all their genetic material.
Non-identical twins and ordinary siblings share approximately half of the genes that vary between people.
Parents and biological children also share approximately half.

Researchers use these differences in genetic relatedness to investigate whether offending has an inherited component.

Genotype and Phenotype

A genotype is a person’s genetic constitution.

A phenotype is the observable result produced by the interaction between genes and the environment.

For example:

A person may inherit genes associated with impulsivity.
Whether impulsive offending develops may depend on parenting, peer groups, education and life experiences.
The observable offending behaviour is therefore not produced by genes alone.

The distinction can be represented as:

Genotype + environment → phenotype

This is important because genetic explanations should not assume that possessing a particular genotype guarantees offending.

Genetic Predisposition

A genetic predisposition is an inherited vulnerability that increases the probability of a characteristic or behaviour.

A predisposition:

Is not a certainty.
May never be expressed.
Can be strengthened or weakened by environmental factors.
May influence some forms of offending more than others.
Usually operates through biological and psychological mechanisms.

A careful statement would be:

Genetic differences may increase a person’s vulnerability to impulsive or aggressive offending.

An inaccurate statement would be:

Some people are born criminals.

The first statement expresses probability. The second is deterministic and unsupported.

What Might Be Inherited?

Genetic explanations do not need to propose a gene for a particular offence.

Genes may influence intermediate characteristics such as:

Impulsivity.
Aggression.
Emotional instability.
Fearlessness.
Poor behavioural inhibition.
Difficulty responding to punishment.
Sensation seeking.

These characteristics may increase offending risk in particular situations.

For example:

A person with an inherited tendency towards impulsivity may be more likely to offend when exposed to peer pressure and immediate rewards.

The genetic vulnerability affects the likelihood of the behaviour, while the social situation influences whether it is expressed.

Offending Is a Complex Behaviour

Offending behaviour is highly varied.

It includes acts that may be:

Impulsive or carefully planned.
Aggressive or non-aggressive.
Committed alone or in a group.
Motivated by financial reward, anger, status or social approval.
Learned through experience.
Influenced by opportunity.

It is therefore unlikely that one genetic factor provides a complete explanation of every offence.

A genetic explanation may be more relevant to:

Impulsive violence.
Reactive aggression.
Persistent antisocial behaviour.
Offending associated with poor emotional control.

It may be less directly relevant to:

Carefully planned financial offending.
Offending learned within a particular group.
Crimes requiring specialist knowledge.
Behaviour shaped primarily by opportunity.

Candidate Genes

A candidate gene is a gene investigated because its biological function could plausibly be connected with a behaviour.

Researchers may identify a gene involved in:

Neurotransmitter regulation.
Emotional processing.
Impulse control.
Stress responses.

They then investigate whether particular variants occur more frequently among people showing antisocial or offending behaviour.

A statistical association does not mean that the gene directly causes the behaviour.

It may:

Contribute only a small amount of risk.
Affect an intermediate characteristic.
Operate only in certain environments.
Be linked with another relevant genetic factor.

The MAOA Gene

The monoamine oxidase A gene, shortened to MAOA, is one genetic factor considered in biological explanations of offending.

The gene is located on the X chromosome and provides instructions for producing the enzyme monoamine oxidase A.

This enzyme is involved in regulating monoamine neurotransmitters, including:

Serotonin.
Dopamine.
Noradrenaline.

AQA mark schemes accept the MAOA gene and evidence from disabling the gene in animals as relevant content when explaining genetic influences on offending.

Low-Activity MAOA

Some people possess a relatively low-activity variant of the MAOA gene.

This is often referred to as MAOA-L.

The proposed chain is:

The person inherits a low-activity MAOA variant.
The variant affects production or activity of the monoamine oxidase A enzyme.
Regulation of monoamine neurotransmitters is altered.
Neural systems involved in emotional control and inhibition may develop or function differently.
Impulsive or aggressive behaviour may become more likely.
In a challenging environment, the risk of offending may increase.

The most important exam point is that MAOA-L is a vulnerability, not an offence-producing switch.

MAOA and Aggressive Offending

The MAOA explanation may be particularly relevant to offending involving:

Impulsive aggression.
Poor emotional control.
Rapid responses to provocation.
Persistent antisocial behaviour.

It does not provide an equally strong explanation for every offence.

For example:

MAOA-related vulnerability might help explain why someone responds violently during a confrontation.

It would provide a less direct explanation for:

Someone who carefully plans a complicated financial offence over several months.

This distinction prevents the genetic explanation from becoming too broad.

Genes May Affect Neural Functioning

Genes can influence behaviour through their effects on biological systems.

A possible pathway is:

Gene variant → enzyme or protein activity → neurotransmitter regulation → brain functioning → behavioural vulnerability

This means genetic and neural explanations are related.

However, they have different emphases:

Genetic explanations focus on inherited biological information.
Neural explanations focus on brain structures, activity and neurotransmission.

The neural processes are developed further in biological functioning associated with offending [Lesson 5: Neural explanations of offending].

Animal Gene-Disabling Evidence

Researchers can investigate genetic mechanisms by disabling or altering a gene in non-human animals.

A gene-disabling study prevents a gene from functioning normally.

If animals with disrupted MAOA functioning show more aggression than animals with normal functioning, this supports the claim that the gene contributes to the regulation of aggressive behaviour.

The advantage of this method is greater control:

The researcher manipulates the gene.
Environmental conditions can be standardised.
Behaviour can be compared with a control group.
Cause and effect can be investigated more directly.

The 2021 AQA mark scheme identifies evidence from disabling the MAOA gene in mice as support for genetic explanations of offending.

Limitations of Animal Evidence

Animal evidence does not demonstrate directly that a genetic variant causes human offending.

Human offences involve:

Knowledge of laws.
Moral decision-making.
Language.
Social learning.
Cultural rules.
Awareness of consequences.
Complex motives.

An animal may display aggression, but it cannot commit an offence in the legal and social sense.

Animal research may therefore support a biological mechanism associated with aggression, but generalisation to human offending must be cautious.

Family Studies

Family studies investigate whether offending or antisocial behaviour occurs more frequently among biological relatives.

The reasoning is:

Biological relatives share genes.
Close relatives share more genes than distant relatives.
If offending has a genetic component, rates should be higher among closer biological relatives.
A pattern of offending across generations may therefore support genetic influence.

Researchers might compare:

Children of people with convictions.
Siblings of offenders.
More distant biological relatives.
Families without known offending histories.

What Family Similarity Can Show

If offending occurs more frequently within some biological families, this is consistent with genetic influence.

However, relatives also frequently share:

Homes.
Parenting.
Socioeconomic conditions.
Peer networks.
Neighbourhoods.
Attitudes towards authority.
Models of offending behaviour.

Family similarity therefore cannot establish whether the resemblance is caused by genes or shared environmental experience.

Twin Studies

Twin studies compare monozygotic twins with dizygotic twins.

Monozygotic twins

Monozygotic twins develop from the same fertilised egg and share effectively all their genetic material.

They are often abbreviated to MZ twins.

Dizygotic twins

Dizygotic twins develop from two separately fertilised eggs.

They share approximately half of the genes that vary between people, like ordinary siblings.

They are often abbreviated to DZ twins.

Concordance Rates

A concordance rate shows the extent to which both members of a pair share a characteristic.

In an offending study, researchers might ask:

If one twin has been convicted, how often has the other twin also been convicted?

If MZ twins have a higher concordance rate than DZ twins, this supports a genetic contribution because MZ twins share more genes.

The logic is:

Greater genetic similarity + greater behavioural similarity = evidence consistent with inheritance

Interpreting Twin Evidence Carefully

Suppose a study produces the following pattern:

Twin type	Concordance for recorded offending
Monozygotic twins	42%
Dizygotic twins	20%

The appropriate conclusion is:

The higher concordance among MZ twins is consistent with a genetic influence on offending.

It would be inaccurate to conclude:

Genes determine offending.

The MZ concordance is not 100%, showing that genetically identical people can have different outcomes.

The Equal Environments Assumption

Twin studies often assume that MZ and DZ twins experience equally similar environments.

This is the equal environments assumption.

However, MZ twins may:

Be treated more similarly.
Spend more time together.
Share more friends.
Be encouraged to dress or behave alike.
Be more likely to identify closely with each other.

Higher concordance among MZ twins might therefore reflect more similar environments as well as greater genetic similarity.

This makes it difficult to calculate the precise contribution of genes.

Offending Records in Twin Research

Twin studies may rely on official records such as:

Arrests.
Convictions.
Prison sentences.
Police contacts.

These are objective in the sense that they are documented.

However, official records do not include every offence.

They are affected by:

Whether offending is detected.
Police decisions.
Prosecution decisions.
Access to legal representation.
Whether a conviction is secured.

Twin concordance may therefore measure similarity in recorded offending, not necessarily similarity in all offending behaviour.

Adoption Studies

Adoption studies attempt to separate genetic and environmental influences.

An adopted person shares:

Genes with biological relatives.
Their rearing environment with adoptive relatives.

Researchers compare the adoptee’s offending with that of:

Biological parents.
Adoptive parents.
Biological siblings.
Adoptive siblings.

The reasoning is:

Similarity to biological relatives supports genetic influence.
Similarity to adoptive relatives supports environmental influence.
Influence from both groups supports interactionism.

Interpreting Adoption Findings

Consider the following pattern:

Adoptees with offending biological relatives show elevated offending rates.
Adoptees with offending adoptive relatives also show elevated rates.
The highest risk occurs when both biological and adoptive risk are present.

This would support an interactionist conclusion:

Inherited vulnerability may be most likely to lead to offending when the person is also raised in a high-risk environment.

Adoption studies can therefore provide evidence for both genes and experience.

Limitations of Adoption Studies

Adoption does not create a perfect separation between nature and nurture.

Possible problems include:

The prenatal environment is shared with the biological mother.
Adoption may occur after early contact with biological relatives.
Agencies may place children in families similar to their biological families.
Contact with biological relatives may continue.
Adoption itself may affect psychological development.
Records may not include undetected offending.

These factors make causal interpretation difficult.

Selective Placement

Selective placement occurs when adoption agencies place children in adoptive homes similar to their biological homes.

Similarity may involve:

Social background.
Ethnicity.
Religion.
Education.
Family structure.

If biological and adoptive environments are similar, researchers may overestimate genetic influence because the environmental separation is incomplete.

Shared and Non-Shared Environments

Family members experience both shared and non-shared environments.

Shared environment

Experiences common to siblings, such as:

Home.
Parenting style.
Neighbourhood.
Family income.

Non-shared environment

Experiences that differ between siblings, such as:

Different peer groups.
Different teachers.
Different treatment by parents.
Different relationships.
Different life events.

Even identical twins may develop different behaviour because of non-shared experiences.

Heritability

Heritability is an estimate of the extent to which variation in a characteristic within a particular population is associated with genetic differences.

Heritability does not mean:

The percentage of one person’s offending caused by genes.
That a characteristic cannot change.
That the same estimate applies in every society.
That the environment is unimportant.

A high heritability estimate can exist alongside strong environmental influence.

For example, genetic differences may affect vulnerability, while environmental conditions determine whether that vulnerability is expressed.

Genetic Vulnerability in an Unfamiliar Scenario

Consider this scenario:

Daniel’s biological father and older biological brother have both been convicted of impulsive violent offences. Daniel has a low-activity MAOA variant. He has not committed an offence and describes his childhood as safe and supportive.

A careful genetic explanation would state:

Daniel may have inherited a vulnerability associated with impulsive aggression.
His biological relatives’ behaviour is consistent with familial influence.
MAOA-L may affect biological systems involved in emotional regulation.
The genetic factor does not make offending inevitable.
Daniel’s safe and supportive environment may reduce the likelihood that the vulnerability is expressed.
His lack of offending challenges genetic determinism.

Applying Genetic Vulnerability to Offending

Consider another scenario:

Callum has a low-activity MAOA variant and experienced repeated childhood adversity. As an adult, he frequently responds violently to minor provocation and has several convictions for assault.

A strong application might state:

Callum may possess an inherited vulnerability associated with reduced regulation of impulsive aggression. His childhood adversity may have acted as an environmental risk factor, increasing the likelihood that the vulnerability was expressed. His assault convictions can therefore be explained through a gene-environment interaction rather than the MAOA variant acting alone.

This answer:

Identifies the genetic vulnerability.
Uses details from the scenario.
Includes the environment.
Avoids saying that the gene forced Callum to offend.

A Poor Application

A weak answer would state:

Callum has the criminal gene, so he commits assault.

This is inaccurate because:

MAOA is not a “criminal gene”.
It does not predict a particular offence.
Many people with a vulnerability do not offend.
Environmental experience is ignored.
The statement is biologically deterministic.

Gene-Environment Interaction

A gene-environment interaction occurs when the effect of a genetic vulnerability depends on environmental experience.

The process may be:

The person inherits a vulnerability.
The environment contains risk or protective factors.
The environment affects whether the vulnerability is expressed.
Offending becomes more or less likely.

Possible environmental risk factors include:

Childhood adversity.
Exposure to violence.
Aggressive role models.
Reinforcement of offending.
Peer pressure.
Educational failure.
Substance misuse.
Chronic stress.

Possible protective factors include:

Stable caregiving.
Education.
Prosocial peers.
Effective emotional support.
Clear boundaries.
Opportunities for achievement.

Diathesis-Stress Model

The gene-environment interaction can be described through the diathesis-stress model.

Diathesis: An inherited vulnerability.
Stress: An environmental trigger or adverse experience.
Outcome: Offending becomes more likely when the vulnerability and stress occur together.

The model can be represented as:

Genetic diathesis + environmental stress → increased risk of offending

Neither factor alone has to be sufficient.

The 2021 AQA mark scheme explicitly identifies childhood experiences, education and other social variables as factors that may mediate biological influences on offending.

Differential Susceptibility

Genetic vulnerability may make some people more responsive to their environment.

A biologically vulnerable person may be:

More harmed by an adverse environment.
More strongly protected by a supportive environment.

This suggests that genes influence sensitivity rather than creating a fixed behavioural destiny.

For exam purposes, the central idea remains:

Genes alter probability, while the environment affects expression.

Protective Environments

A genetic explanation should not focus only on risk.

A supportive environment may:

Teach emotional regulation.
Reinforce non-offending behaviour.
Provide stable relationships.
Reduce exposure to aggressive models.
Offer legitimate rewards and opportunities.
Encourage problem-solving.

This helps explain why people with similar biological vulnerabilities can have very different outcomes.

Genetic and Neural Explanations Compared

Genetic explanation	Neural explanation
Focuses on inherited DNA and gene variants	Focuses on brain structure, activity and neurotransmission
Examines family, twin and adoption patterns	Examines brain scans and physiological measures
MAOA may affect enzyme production	Neural systems may affect inhibition and decision-making
Explains biological vulnerability	Explains a possible mechanism through which vulnerability operates
Does not directly identify current brain function	Does not establish that differences were inherited

The explanations are compatible.

Genes may affect neural development, while experience can also change neural functioning.

Genetic and Social Learning Explanations Compared

Genetic explanations locate vulnerability partly within inherited biology.

Learning offending through association and reinforcement [Lesson 9: Differential association theory] locates the origin mainly within social experience.

Genetic explanation	Differential association theory
Offending vulnerability may be inherited	Offending is learned through interaction
Focuses on biological predisposition	Focuses on exposure to criminal values
Uses twin, adoption and gene research	Uses social relationships and reinforcement
Explains individual vulnerability	Explains the content and methods of offending
May struggle to explain the particular offence	Can explain how techniques and attitudes are acquired

The explanations may interact. A person with high impulsivity may be especially likely to act on offending attitudes learned from peers.

Genetic and Personality Explanations

Genetic vulnerability can also be linked with inherited personality characteristics associated with offending [Lesson 6: Eysenck’s theory of the criminal personality].

Eysenck proposed that personality traits have a biological basis.

A distinction is still needed:

Genetic explanations focus broadly on inherited vulnerability and candidate genes.
Eysenck’s theory identifies a particular combination of personality dimensions.

Do not replace a genetic explanation with a description of extraversion, neuroticism and psychoticism unless the question permits both explanations.

Strength: Family, Twin and Adoption Evidence

A strength of genetic explanations is that several research methods can investigate inherited influence.

Family studies examine whether offending clusters among relatives.
Twin studies compare people with different levels of genetic similarity.
Adoption studies separate biological relationship from rearing environment.
Molecular research investigates particular genes such as MAOA.
Animal studies allow more direct manipulation.

If different methods point towards inherited influence, this provides converging evidence.

However, each method has limitations, so agreement does not prove that genes directly cause offending.

Strength: Twin Comparisons Provide a Clear Prediction

Twin research produces a testable prediction:

If genetic influence is important, MZ twins should show greater concordance than DZ twins.

This allows the genetic explanation to be investigated empirically.

The prediction is falsifiable because researchers could find:

Similar concordance among MZ and DZ twins.
Stronger relationships with environmental similarity.
No meaningful familial pattern.

The scientific value depends on accurate records and valid assumptions about twin environments.

Strength: Adoption Research Separates Influences

Adoption studies are valuable because biological and environmental relationships are partially separated.

They may show:

Genetic influence through resemblance to biological relatives.
Environmental influence through resemblance to adoptive relatives.
Interaction when biological and adoptive risk combine.

This makes adoption evidence particularly useful for rejecting a simple nature-or-nurture choice.

Strength: Biological Mechanisms Can Be Investigated

MAOA research provides a possible mechanism linking genes with behaviour.

Rather than simply stating that offending “runs in families”, researchers can investigate:

A particular gene.
Its effect on an enzyme.
Consequences for neurochemical regulation.
Associations with impulsive or aggressive behaviour.

This increases the explanatory depth of the genetic account.

The mechanism also generates testable predictions for animal and human research.

Limitation: Genes Do Not Directly Code for Crime

Genes code for proteins and biological processes, not socially defined offences.

Whether a behaviour is classified as an offence depends on:

Law.
Culture.
Historical period.
Social context.
The person’s circumstances.

A genetic factor might influence impulsivity or aggression, but it cannot contain instructions to commit a legally defined act.

The explanation is therefore more convincing when it focuses on inherited psychological vulnerabilities rather than an inherited criminal identity.

Limitation: Different Forms of Offending

A genetic explanation may not apply equally to every type of offending.

MAOA-related vulnerability may be more relevant to:

Reactive violence.
Impulsive assault.
Aggressive antisocial behaviour.

It may be less relevant to:

Planned fraud.
Deliberate cybercrime.
Financial offences.
Offending learned through a criminal organisation.

Treating all offenders as biologically similar would ignore the diversity of offending behaviour.

Limitation: Shared Environment in Family Studies

Families share genes and environments.

If a child resembles an offending parent, this could result from:

Genetic inheritance.
Modelling.
Direct reinforcement.
Shared deprivation.
Similar peer networks.
Family attitudes towards the law.

Family studies therefore demonstrate familial transmission but cannot reveal whether that transmission is biological or social.

Limitation: Equal Environments in Twin Studies

MZ twins may experience more similar environments than DZ twins.

They may:

Be treated more alike.
Have more shared friends.
Spend more time together.
Develop stronger mutual identification.

Higher concordance may therefore be partly environmental.

This makes it difficult to convert twin differences into a precise genetic explanation.

Limitation: Adoption Is Not a Perfect Natural Experiment

Adoption studies reduce shared upbringing but do not remove environmental overlap entirely.

Relevant complications include:

Prenatal influence.
Early life before adoption.
Selective placement.
Continued biological-family contact.
Adoption-related experiences.

The study design is useful but cannot isolate genes with complete certainty.

Limitation: Official Records Are Incomplete

Genetic research often uses convictions or official offending records.

These data measure detected and recorded behaviour.

They may be affected by:

Police attention.
Reporting.
Prosecution.
Legal representation.
Court decisions.
Social inequality.

Some offenders are never caught, while some groups may be more likely to enter official records.

This may reduce the validity and representativeness of findings.

Limitation: Correlation and Causation

Human genetic studies are usually correlational.

Researchers cannot:

Randomly assign people to genetic variants.
Experimentally alter a person’s genes.
Control all experiences from birth.
Require people to commit offences.

An association between a gene and offending does not establish causation.

The gene might be associated with:

Aggression.
Impulsivity.
Substance misuse.
Another biological factor.

The offence itself may result from additional social and situational influences.

Limitation: Generalising from Animals

Gene-disabling studies allow stronger causal investigation, but they involve non-human animals.

Animals do not:

Understand criminal law.
Make legal or moral judgements.
Commit socially defined offences.
Experience the full complexity of human relationships and institutions.

Animal evidence supports a possible biological mechanism, not a complete explanation of human offending.

AQA identifies this generalisation problem as a relevant evaluation of biological explanations.

Limitation: Reductionism

Genetic explanations may be criticised for biological reductionism.

They reduce complex offending behaviour to:

DNA.
Gene variants.
Enzymes.
Neurotransmitter regulation.
Inherited traits.

This may overlook:

Poverty.
Education.
Family relationships.
Peer groups.
Social learning.
Cognitive distortions.
Opportunity.
Legal and cultural context.

Reductionism can be useful because it produces measurable variables and testable mechanisms.

However, offending is unlikely to be explained fully at the genetic level.

This connects with the strengths and limitations of biological reductionism [Lesson 5: Holism and reductionism].

Limitation: Biological Determinism

A genetic explanation may be interpreted as biologically deterministic.

This would suggest that:

Genes control offending.
The individual has little choice.
Behaviour cannot be changed.
Responsibility should be reduced.

This interpretation is problematic because:

Genetic associations are probabilistic.
Identical twins are not perfectly concordant.
Environmental interventions can affect behaviour.
People with genetic vulnerabilities do not necessarily offend.

A vulnerability model is less deterministic than claiming that genes directly cause criminal behaviour.

This issue connects with biological causation and personal responsibility [Lesson 3: Free will and determinism].

Moral and Legal Responsibility

Genetic explanations raise difficult questions for the criminal justice system.

If an offender has a biological vulnerability:

Should this reduce responsibility?
Should it affect sentencing?
Does vulnerability make the behaviour less voluntary?
Should support or treatment be prioritised?
How should risk be assessed?

A genetic vulnerability does not remove all choice or responsibility.

Many people may possess the same vulnerability without offending. Behaviour remains influenced by decisions, learning and social circumstances.

The AQA mark scheme accepts moral and legal responsibility, blame and the possibility of change as important implications of biological explanations.

Socially Sensitive Implications

Genetic research into offending is socially sensitive.

Possible consequences include:

Labelling people as future offenders.
Discrimination based on family history.
Stigmatising biological relatives.
Treating genetic risk as proof of dangerousness.
Increased surveillance.
Reduced expectations of rehabilitation.
Misuse of genetic testing.

A gene associated with risk cannot predict accurately whether one individual will offend.

Researchers must communicate:

Genetic vulnerability is not genetic destiny.

Problems with Screening

Using genetic screening to identify possible offenders would be highly problematic.

A screening programme could produce:

False positives, where people are labelled despite never offending.
False negatives, where people without the selected variant offend.
Discrimination.
Anxiety.
Breaches of privacy.
Unjustified intervention.

Because offending is influenced by many factors, a single genetic result would have very limited predictive value.

Implications for Rehabilitation

A strongly deterministic interpretation might suggest that genetically influenced offending cannot be changed.

However, gene-environment interaction suggests the opposite.

If the environment affects expression of vulnerability, interventions may reduce risk through:

Education.
Emotional-regulation training.
Stable relationships.
Prosocial opportunities.
Treatment for substance misuse.
Support during childhood.
Reduced exposure to aggressive models.

Genetic influence therefore does not make rehabilitation pointless.

Practical Value

Understanding biological vulnerability might help psychologists:

Identify people needing early support.
Develop interventions for impulsivity.
Improve emotional-regulation programmes.
Combine biological and social risk assessments.
Avoid relying on punishment alone.

The practical value depends on avoiding deterministic labels and protecting individual rights.

Alternative Explanation: Differential Association

Learning offending values and techniques from close groups [Lesson 9: Differential association theory] may explain aspects that genes cannot.

Differential association can explain:

Which offences are learned.
Which techniques are used.
Why offending is approved within a group.
How criminal attitudes are reinforced.

A genetic explanation may explain vulnerability, while differential association explains the content and social meaning of the behaviour.

Alternative Explanation: Cognitive Processes

Genetic explanations do not directly explain:

Hostile interpretations.
Victim blaming.
Minimising harm.
Pre-conventional moral reasoning.

These are considered in:

moral decision-making in offenders [Lesson 7: Moral reasoning]
biased thinking about offending [Lesson 8: Cognitive distortions]

A comprehensive explanation may combine biological vulnerability with learned and cognitive processes.

An Interactionist Explanation

An interactionist account may include several stages:

A person inherits a vulnerability associated with impulsivity.
They experience inconsistent parenting or childhood adversity.
They associate with peers who reward offending.
Aggressive or criminal behaviour is modelled.
Immediate rewards strengthen the behaviour.
Cognitive distortions justify the offence.
A provocative situation triggers the behaviour.

This explanation is more complex, but offending itself is complex.

Overall Evaluation

Genetic explanations are supported by patterns in family, twin, adoption, molecular and animal research. They provide a possible account of why some individuals may be more vulnerable to impulsivity, aggression and antisocial behaviour.

The MAOA gene offers a plausible route through which inherited differences may affect biological systems involved in behavioural regulation. However, MAOA is not a “criminal gene”, and animal aggression cannot be equated directly with human offending.

Human studies cannot completely separate genes from shared environments, while official records may not accurately represent all offending. Genetic explanations are also reductionist and can have harmful deterministic and socially sensitive implications.

The most defensible conclusion is that genes contribute to vulnerability rather than determining behaviour. Offending is most convincingly explained through an interaction between biological predispositions and environmental experiences.

Key Words 🔑

Key word	Student-friendly definition	How it may be used in an exam
Genetic explanation	An explanation proposing that inherited biological differences contribute to behaviour	Introduce the biological explanation of offending
Gene	A section of DNA involved in producing a biological characteristic or process	Explain how information is inherited
DNA	The material carrying genetic information	Explain biological transmission
Genotype	A person’s genetic constitution	Distinguish inherited information from observable behaviour
Phenotype	The observable result of genetic and environmental interaction	Explain why the same genotype may produce different outcomes
Genetic predisposition	An inherited vulnerability increasing the probability of a behaviour	Avoid claiming that genes make offending inevitable
Genetic vulnerability	A biological risk that may be expressed under particular environmental conditions	Apply the explanation to an offender scenario
Candidate gene	A gene investigated because its function may relate to a particular behaviour	Introduce MAOA research
MAOA gene	A gene providing instructions for the monoamine oxidase A enzyme	Explain a possible genetic vulnerability
MAOA-L	A relatively low-activity variant of the MAOA gene	Link altered biological regulation with impulsive aggression
Monoamine oxidase A	An enzyme involved in regulating monoamine neurotransmitters	Explain the biological route through which MAOA may operate
Family study	Research examining whether a characteristic occurs among biological relatives	Investigate familial transmission
Twin study	Research comparing twins with different levels of genetic similarity	Examine inherited influence
Monozygotic twins	Twins sharing effectively all their genetic material	Explain why they are compared with DZ twins
Dizygotic twins	Twins sharing approximately half of the genes that vary between people	Provide the comparison group
Concordance rate	The extent to which both members of a pair share a characteristic	Interpret twin findings
Equal environments assumption	The assumption that MZ and DZ twins experience equally similar environments	Evaluate twin evidence
Adoption study	Research comparing an adoptee with biological and adoptive relatives	Separate inherited and environmental influence
Selective placement	Placing adoptees in homes similar to their biological families	Evaluate adoption research
Heritability	An estimate of genetic contribution to variation within a population	Explain group-level genetic influence carefully
Gene-environment interaction	The combined effect of inherited vulnerability and experience	Evaluate a purely genetic account
Diathesis-stress model	The idea that an underlying vulnerability is expressed under environmental stress	Apply genetic vulnerability to offending
Gene-disabling study	Research preventing a gene from functioning normally	Explain animal evidence involving MAOA
Biological determinism	The view that biological factors govern behaviour	Evaluate implications for choice and responsibility
Biological reductionism	Explaining behaviour through genes and other basic biological processes	Evaluate the limited level of explanation
Social sensitivity	The possibility that research has consequences for individuals or groups	Discuss labelling, screening and discrimination

Hints from the Examiner Reports 💡

Keep Genetics Separate from Neural Explanations

Examiner hint: Genetic and neural explanations are related, but they are not interchangeable.

For a question focused on genetics, prioritise:

Inheritance.
Genes and DNA.
MAOA.
Family, twin and adoption evidence.
Concordance.
Genetic vulnerability.
Gene-environment interaction.

A paragraph describing the prefrontal cortex without establishing an inherited mechanism is neural rather than genetic.

Use the Term Vulnerability

Examiner hint: Avoid suggesting that genes make offending inevitable.

Strong phrasing includes:

“Creates a predisposition.”
“Increases risk.”
“May be expressed.”
“Interacts with environmental factors.”
“Is associated with.”

Avoid:

“Causes crime.”
“Criminal gene.”
“Born offender.”
“Cannot control their behaviour.”

Explain the Logic of Twin Studies

Do not merely state that researchers study twins.

A developed explanation is:

MZ twins share more genes than DZ twins. If MZ twins show higher concordance for offending, this is consistent with a genetic contribution.

Then evaluate the shared-environment problem.

Interpret Concordance Correctly

Concordance below 100% is important.

It suggests that:

Genes cannot provide the complete explanation.
Non-shared environments influence behaviour.
The same inherited vulnerability can produce different outcomes.

Do not treat higher MZ concordance as proof of genetic determinism.

Apply Both Genetic and Environmental Details

For an application question, use:

The biological or family evidence.
The relevant vulnerability.
The person’s environmental risk or protection.
The observed form of offending.
A cautious conclusion.

For example:

The MAOA variant may create vulnerability, while childhood adversity may act as a trigger. The combination could increase the likelihood of impulsive assault.

Use Animal Evidence Carefully

The official mark scheme accepts evidence from MAOA gene-disabling studies in mice. It also accepts the criticism that animal findings may not generalise well to human offending.

A developed point is:

Disabling MAOA allows researchers to investigate cause and effect under controlled conditions. However, the measured outcome is animal aggression, not legally and socially defined human offending, so generalisation is limited.

Develop Social Mediation

The 2021 mark scheme recognises childhood experiences, education and other social influences as factors mediating biological vulnerability.

This means evaluation should not stop at:

The environment is also important.

Explain how the environment changes whether the vulnerability is expressed.

Develop Broader Issues

Do not simply write:

The explanation is deterministic and reductionist.

Develop each point:

It is biologically deterministic if genes are presented as controlling offending. This may reduce perceived responsibility and encourage pessimism about rehabilitation. However, incomplete concordance and gene-environment interaction challenge this interpretation.

Focus Evaluation on the Explanation

Methodological evaluation earns value when it affects the genetic conclusion.

For example:

Official conviction records omit undetected offending. Concordance based on these records may therefore underestimate or distort similarity between twins, weakening conclusions about genetic influence.

Balance AO1 and AO3

The 2021 biological-explanations question allocated six marks to AO1 and ten marks to AO3. High-level answers therefore needed accurate knowledge alongside thorough and effective evaluation.

A useful 16-mark structure is:

Explain inherited vulnerability.
Explain MAOA.
Explain family, twin or adoption evidence.
Evaluate shared environments and research methods.
Develop gene-environment interaction.
Discuss reductionism and determinism.
Consider legal and socially sensitive implications.
Reach a balanced conclusion.

The related examiner report noted that the strongest 16-mark answers were detailed and well argued. It also stressed that application should be underpinned by psychological knowledge rather than unsupported commonsense statements.

Common Mistakes ⚠️

Mistake 1

Mistake: Saying there is a single criminal gene.

Why this is incorrect:

The source material supports genetic vulnerability and MAOA as one possible factor, not a gene that directly produces every form of offending.

How to improve:

Refer to inherited predispositions affecting characteristics such as impulsivity or aggression.

Mistake 2

Mistake: Saying MAOA is a neurotransmitter.

Why this is incorrect:

MAOA is a gene. It provides instructions for producing the monoamine oxidase A enzyme.

How to improve:

Use the sequence:

MAOA gene → enzyme activity → neurotransmitter regulation → behavioural vulnerability

Mistake 15

Mistake: Using reductionism or determinism as unexplained labels.

Why this is incomplete:

Evaluation marks reward developed reasoning.

How to improve:

Explain what the account overlooks and why the issue affects responsibility, validity or rehabilitation.

Exam-Style Questions ✍️

Question 1

What is meant by a genetic predisposition? [2 marks]

Question 2

Explain why a gene associated with offending should be described as a vulnerability rather than a direct cause. [2 marks]

Question 3

Explain how twin studies may be used to investigate genetic explanations of offending. [4 marks]

Question 4

Outline the possible role of the MAOA gene in offending behaviour. [4 marks]

Question 5

Ellis has a low-activity MAOA variant. Ellis experienced a stable childhood, has supportive relationships and has never been convicted of an offence.

Use your knowledge of genetic explanations to explain why Ellis may not show offending behaviour. [4 marks]

Question 6

Researchers examine recorded offending among two groups of twin pairs.

Twin type	Concordance for recorded offending
Monozygotic twins	44%
Dizygotic twins	19%

Describe the difference in concordance and explain what the findings suggest. Identify one reason why the findings do not prove that offending is genetically determined. [5 marks]

Question 7

Tariq has a low-activity MAOA variant and experienced serious childhood adversity. He frequently responds impulsively to provocation and has several convictions for assault.

Use your knowledge of genetic vulnerability to explain Tariq’s offending. [4 marks]

Question 8

Explain one strength and one limitation of adoption studies used to investigate genetic explanations of offending. [6 marks]

Question 9

Briefly evaluate genetic explanations of offending behaviour. [4 marks]

Question 10

Discuss genetic explanations of offending behaviour. [16 marks]

Answers and Mark Scheme

Question 1

Award one mark for each of the following:

An inherited biological vulnerability or tendency.
It increases the probability of behaviour but does not make the behaviour inevitable.

Maximum: 2 marks

Question 2

Award marks as follows:

One mark for explaining that many people with the genetic factor do not offend.
One mark for explaining that environmental, social or psychological factors affect whether the vulnerability is expressed.

Maximum: 2 marks

Question 3

Award one mark for each relevant point, up to four marks:

Twin studies compare monozygotic and dizygotic twins.
MZ twins share effectively all their genetic material.
DZ twins share approximately half of the genes that vary between people.
Researchers calculate concordance for offending.
Higher MZ concordance would support a genetic contribution.
Concordance below 100% suggests environmental influence.
The interpretation depends on the equal environments assumption.

A full-mark answer should explain the logic of the comparison.

Question 4

Award one mark for each relevant point, up to four marks:

MAOA is a gene located on the X chromosome.
It provides instructions for producing the monoamine oxidase A enzyme.
The enzyme is involved in regulating monoamine neurotransmitters.
A low-activity variant may alter biological regulation.
This may contribute to impulsivity, aggression or poor emotional control.
These characteristics may increase vulnerability to some offending.
The gene does not make offending inevitable.
Environmental factors affect whether the vulnerability is expressed.

Question 5

Award up to four marks for effective application:

Ellis may possess an inherited vulnerability associated with MAOA-L.
A vulnerability increases risk rather than determining behaviour.
Ellis’s stable childhood may act as a protective environmental factor.
Supportive relationships may encourage emotional regulation and prosocial behaviour.
The absence of environmental stressors may reduce expression of the vulnerability.
Ellis illustrates a gene-environment interaction.
The scenario challenges biological determinism.

Do not award full marks for stating only that the environment is more important.

Question 6

Award one mark for accurately describing the difference:

Concordance is 25 percentage points higher among MZ twins.

44%−19%=25 percentage points

Award up to two marks for interpretation:

MZ twins share more genes.
Their higher concordance supports a genetic contribution to recorded offending.
Genetic similarity is associated with behavioural similarity.

Award up to two marks for a limitation:

MZ twins may experience more similar environments.
Official records do not include undetected offending.
Concordance among MZ twins is not 100%.
Non-shared environments may produce different outcomes.
The findings are correlational and do not establish causation.

Question 7

Award up to four marks for effective application:

Tariq may possess an inherited vulnerability associated with MAOA-L.
The variant may affect biological regulation linked with impulsive aggression.
His impulsive responses to provocation are consistent with this vulnerability.
Childhood adversity may act as an environmental stressor.
The combination illustrates a gene-environment interaction.
His assault offending is more likely because both vulnerability and risk experience are present.
The explanation does not claim that the gene forced Tariq to offend.

Question 8

Award up to three marks for one developed strength and three marks for one developed limitation.

Possible strength:

Adoption studies partially separate genes from upbringing because adoptees share genes with biological relatives but a home environment with adoptive relatives. Greater similarity to biological relatives would therefore support inherited influence. Similarity to both groups can also reveal gene-environment interaction.

Possible limitation:

Adoption does not separate nature and nurture completely. Adoptees share a prenatal environment with their biological mother, may experience care before adoption and may be placed in families similar to their biological family. Apparent genetic similarity could therefore contain environmental influence.

Other creditworthy limitations include:

Continued contact with biological relatives.
Incomplete official records.
Small or selective samples.
Ethical and practical difficulties.

Question 9

Award up to four marks for clear and effective evaluation.

Possible content:

Support from family, twin, adoption or MAOA evidence.
Higher MZ than DZ concordance.
Shared-environment problems.
Adoption does not separate influences perfectly.
Animal research may not generalise to human offending.
Genetic associations do not establish causation.
Gene-environment interaction.
Biological reductionism.
Biological determinism.
Legal and socially sensitive implications.
Limited explanation of non-aggressive or carefully planned offending.

Example full-mark response:

Higher concordance for offending among MZ than DZ twins supports a genetic contribution because MZ twins share more genes. However, MZ twins may also be treated more similarly, so the difference cannot be attributed entirely to inheritance. Incomplete concordance further suggests that genes create vulnerability rather than determining offending.

Question 10

A high-level response should include accurate knowledge and developed evaluation.

Indicative AO1 content

Genes and DNA.
Inherited biological vulnerability.
Genotype and phenotype.
Genetic predisposition.
Intermediate characteristics such as impulsivity or aggression.
Candidate genes.
MAOA gene.
Low-activity MAOA variant.
Enzyme and neurotransmitter regulation.
Family studies.
MZ and DZ twins.
Concordance rates.
Adoption studies.
Genetic and environmental risk.
Gene-environment interaction.
Diathesis-stress model.
Application to offending behaviour.

Indicative AO3 content

Family, twin and adoption evidence.
Converging evidence from several methods.
Evidence from MAOA or animal gene-disabling research.
Twin equal-environments problem.
Shared environment within families.
Adoption and selective placement.
Prenatal and early environmental influence.
Incomplete official offending records.
Correlation and cause-and-effect problems.
Difficulty generalising from animal aggression to human offending.
Different explanations for different offence types.
Genes influencing vulnerabilities rather than offences directly.
Gene-environment interaction.
Biological reductionism.
Biological determinism.
Moral and legal responsibility.
Socially sensitive implications.
Problems with genetic screening.
Implications for rehabilitation.
Comparison with neural and psychological explanations.
Need for an interactionist conclusion.

Thirteen to sixteen marks: Knowledge is accurate and generally detailed. Discussion is thorough, focused and effective. Evidence is used to construct arguments, methodological issues are explained and specialist terminology is precise.

Nine to twelve marks: Knowledge is mostly accurate and discussion is generally effective. Genetic vulnerability and relevant evidence are explained, although some evaluation points may lack development or precision.

Five to eight marks: Some relevant knowledge is present, but the response is mainly descriptive. Evidence may be listed without explanation, or evaluation may be generic.

One to four marks: Knowledge is very limited or confused. The answer may present a single “criminal gene”, confuse genetic and neural explanations or provide little relevant evaluation.