What is the primary difference between Monozygotic (MZ) and Dizygotic (DZ) twins in genetic research?

MZ twins share 100% of their genetic material, while DZ twins share approximately 50%. This difference allows researchers to isolate the impact of genetics by comparing how much more similar MZ twins are regarding a specific trait.

How does the Diathesis-Stress model explain the development of addiction?

It suggests that addiction occurs when a biological vulnerability (diathesis) interacts with environmental triggers (stress). Without the environmental trigger, the biological risk may never manifest as a clinical disorder.

What is the difference between a 'genetic cause' and a 'genetic vulnerability'?

A genetic cause implies a direct, deterministic link where the gene guarantees the outcome. A vulnerability means the genes create a predisposition or increased risk, but environmental factors still play a critical role in the outcome.

Why is it a mistake to assume that a high concordance rate in MZ twins proves a purely genetic cause?

MZ twins often share a more similar environment than DZ twins because they look identical and may be treated more similarly by parents and peers. This 'equal environments' assumption can lead to overestimating the genetic influence.

What is the 'single gene fallacy' in the context of addiction research?

It is the incorrect belief that a single gene is responsible for complex behaviors like addiction. In reality, addiction is polygenic, involving many genes that influence various traits like reward sensitivity and impulse control.

Why can't correlational research in genetics establish a definitive cause-and-effect relationship?

Correlation only shows that a genetic marker and a behavior appear together; it doesn't prove the gene causes the behavior. Third variables, such as shared environmental stressors or personality traits, might be the actual drivers.

Define 'Concordance Rate' in the context of biological risk factors.

It is the percentage of twin pairs or family members who both exhibit a particular trait or disorder. It is used to estimate the heritability of that trait by comparing different levels of genetic relatedness.

What does 'Polygenic' mean in relation to addiction?

It means that the risk for addiction is influenced by the combined effect of many different genes, rather than being controlled by a single gene locus.

What is 'Heritability'?

Heritability is a measure of how much of the phenotypic variation in a specific population can be attributed to genetic variation among individuals in that population.

How might inherited personality traits act as a biological risk factor for addiction?

Traits like high impulsivity or sensation-seeking have a biological basis in brain structure and chemistry. If these traits are inherited, they can lead an individual to engage in risky behaviors that increase the chance of addiction.

Biological Risk Factors | AQA A-Level Psychology

Addiction: Option Topic (Section D)

Biological Risk Factors

Summary

Biological risk factors for addiction primarily center on genetic vulnerability, which suggests that inherited physiological or neurological characteristics increase an individual's predisposition to developing addictive behaviors. By analyzing concordance rates in twin and family studies, researchers can estimate the extent to which genetics contribute to the risk of substance abuse or behavioral addictions compared to environmental influences.

1. Definition & Core Concepts

Genetic Vulnerability: This refers to an inherited predisposition that makes an individual more susceptible to developing a disorder, such as addiction, when exposed to certain environmental triggers.
Inherited Characteristics: These are biological traits passed from parents to offspring through DNA, which may influence brain chemistry, specifically the reward system involving dopamine.
Risk vs. Certainty: Having a genetic vulnerability does not guarantee the development of an addiction; rather, it increases the statistical likelihood compared to the general population.

2. Research Methodologies

Twin Studies: Psychologists compare Monozygotic (MZ) twins, who share 100% of their DNA, with Dizygotic (DZ) twins, who share approximately 50%, to isolate genetic effects.
Concordance Rates: This is a measure of the probability that if one twin has a specific trait or disorder, the other twin will also have it. Higher rates in MZ twins compared to DZ twins strongly suggest a genetic component.
Family Linkage Studies: These involve mapping DNA sequences across multiple generations of a family to identify specific gene variants that correlate with addictive behaviors.

A bar chart comparing concordance rates between MZ and DZ twins. The significantly higher bar for MZ twins illustrates the influence of shared genetics on the risk of developing a trait.

3. Underlying Principles: The Interactionist Approach

Diathesis-Stress Model: This framework posits that addiction results from a combination of a biological 'diathesis' (vulnerability) and environmental 'stress' (triggers like trauma or peer pressure).
Polygenic Inheritance: Addiction is rarely caused by a single 'addiction gene'; instead, it involves multiple genes that each contribute a small amount to the overall risk profile.
Epigenetics: This field explores how environmental factors can 'switch' certain genes on or off, further complicating the relationship between biology and behavior.

4. Key Distinctions

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions