Biological: Genetic Explanation (AQA A-Level Psychology): Revision Notes
Biological: Genetic explanation
Introduction
The genetic explanation proposes that schizophrenia is transmitted through hereditary means - passed down through genes from family members. This approach suggests that whilst there is no single 'schizophrenic gene', multiple genes work together to increase an individual's vulnerability to developing the disorder.
The genetic explanation forms part of the broader biological approach, which views schizophrenia as resulting from physiological processes rather than psychological or environmental factors alone.
Core principles of genetic explanation
The genetic approach to understanding schizophrenia is built on several fundamental concepts that explain how hereditary factors contribute to the development of this complex mental disorder.
Key Principles of Genetic Inheritance in Schizophrenia:
- Polygenic inheritance: Multiple genes contribute to schizophrenia risk rather than one single gene
- Increased vulnerability: Genes don't guarantee the development of schizophrenia but increase susceptibility
- Heritability: The disorder can be passed from parents to offspring through genetic material
- Gene-environment interaction: Genetic predisposition may require environmental triggers to manifest as the disorder
Research evidence
Research into the genetic basis of schizophrenia has employed various methodological approaches, each providing valuable insights into the hereditary nature of this disorder.
Twin studies
Twin studies compare concordance rates (the likelihood that both twins will develop schizophrenia) between identical and non-identical twins to assess genetic influence.
Research Example: Gottesman and Shields (1976)
This landmark study reviewed five twin studies and found concordance rates between 75% and 91% for monozygotic (identical) twins who had severe forms of schizophrenia. This suggests a strong genetic component, as identical twins share 100% of their DNA.
Research Example: Torrey et al. (1994)
Researchers examined evidence from twin studies and discovered that when one identical twin develops schizophrenia, there is a 28% chance the other twin will also develop the condition. This supports the hereditary nature of the disorder.
Family and adoption studies
Family and adoption studies provide crucial evidence by separating genetic influences from environmental factors, allowing researchers to examine the relative contributions of nature versus nurture.
Research Example: Kety and Ingraham (1992)
Found that prevalence rates of schizophrenia were ten times higher among genetic relatives compared to adoptive relatives of people with schizophrenia. This indicates that genetics plays a more substantial role than environmental upbringing.
Varma and Sharma (1993) discovered a concordance rate of 35% for first-degree relatives of individuals with schizophrenia, compared with only 9% in first-degree relatives of people without the disorder.
Parnas et al. (1993) conducted a longitudinal family study revealing that 16% of children whose mothers had schizophrenia later developed the disorder, compared with just 2% of children whose mothers did not have schizophrenia.
Gene-mapping studies
Modern research has moved beyond family studies to identify specific genetic markers, utilising advanced molecular techniques to pinpoint exact genetic locations associated with schizophrenia risk.
Research Example: Gurling et al. (2006)
Used family studies to identify that schizophrenia was associated with chromosome 8p21-22, with the PCMI gene implicated in susceptibility to the disorder.
Research Example: Benzel et al. (2007)
Employed gene mapping to find evidence that NRG3 gene variants interact with both NRG1 and ERBB4 gene variants, creating susceptibility to developing schizophrenia through genetic interaction.
Avramopoulos et al. (2013) sequenced genes associated with the neuregulin signalling pathway, which transmits signals within the nervous system. They found that families with high levels of schizophrenia had multiple neuregulin signalling-related variants, whilst others had none. Patients with these variants experienced more hallucinations but less cognitive impairment.
The Schizophrenia Working Group of the Psychiatric Genomics Consortium (2014) analysed DNA from 36,989 patients with schizophrenia and 113,000 people without the disorder. They identified 128 independent genetic variations at 108 locations on human chromosomes that contribute most to developing schizophrenia, with 83 previously unidentified associations.
Evaluation
Strengths
The genetic explanation for schizophrenia has several compelling advantages that strengthen its scientific credibility and practical value.
Strengths of the Genetic Approach:
- Strong empirical support: Twin studies consistently show higher concordance rates in identical twins compared to non-identical twins, providing robust evidence for genetic influence
- Cross-cultural validity: Genetic findings appear consistent across different populations and cultures
- Scientific methodology: Modern gene-mapping techniques offer precise identification of specific genetic markers
- Practical applications: Gene mapping potentially allows for early identification of high-risk individuals
Limitations
Despite its strengths, the genetic explanation faces several significant challenges that limit its explanatory power as a complete account of schizophrenia.
Environmental factors ignored: Twin studies suggest genetic influence but fail to consider environmental and socio-psychological factors. Both twins in identical pairs share similar environments, making it difficult to separate genetic from environmental influences.
Incomplete concordance: If schizophrenia were purely genetic, concordance rates between identical twins would be 100%. The fact that rates range from 58% to as low as 11% suggests environmental factors remain important.
Diathesis-stress model support: Research findings actually support the diathesis-stress model, where individuals inherit different levels of genetic predisposition, but environmental triggers ultimately determine whether the disorder develops.
Research methodology concerns: Leo (2006) argues that adoption study evidence is not convincing due to small sample sizes, making generalisation difficult. Many biological relatives with schizophrenia were distant relatives with low biological similarity.
Bias in research presentation: Hedgecoe (2001) believes scientists have portrayed schizophrenia as a genetic disease using evidence from twin and adoption studies in a biassed manner, producing a narrative that subtly prioritises genetic explanations.
Ethical and social implications: Gene mapping raises socially sensitive and ethical concerns about genetic testing and potential discrimination against individuals identified as high-risk.
Key Points to Remember:
- The genetic explanation proposes that schizophrenia is transmitted through hereditary means via multiple genes working together
- Twin studies show higher concordance rates in identical twins (28-91%) compared to the general population, supporting genetic influence
- Gene-mapping studies have identified specific genetic markers including the PCMI gene and neuregulin signalling pathway variants
- Environmental factors remain important as concordance rates are never 100%, supporting the diathesis-stress model
- Modern research suggests genetic predisposition creates vulnerability that requires environmental triggers to manifest as schizophrenia