- Aim: To find out the extent of similarities between MZ and DZ twins in diagnosis of alcohol abuse/dependance
- Method: Male MZ and DZ twins were interviewed about their alcohol use
- Results: MZ twins- 77% concordancy, DZ twins- 54% concordancy
- Conclusion: The more closely related a person is , the higher the risk of devloping alcoholism themselves- supports hereditary explanation
- Evaluation: MZ twins don't show 100% concordancy, suggesting other factors are influencing outcome e.g. social influence and personality. Results may be due to twins sharing their environment and experiences as opposed to their genetic make up
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- Aim: To investigate the possible inheritance of type 1 and type 2 alcoholism in males
- Method: 1,724 adopted Swedish males were studied. The drinking habits of the sons, their biological fathers and their apoptive fathers were investigated
- Results: The son was more likely to abuse alcohol if their biological father did, 18% of sons tht abused alcohol, their biological fathers did too compared to 4% whose biological fathers didn't
- Conclusion: Supports herditary explanation as it suggests that the genes the sons shared with their biological fathers were resposible
- Evaluaton: Large sample- increases validitiy, all ppts from Sweden- can't be generalised, results showed that the largest percentage of sons were alcohol abusers when both their biological and adoptive fathers were heavy drinkers also- suggest environmental factors
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- Aim: To find how sensitivity varies between sons of alcoholic and non alcoholic fathers
- Method: Ppts were invited to take part in a drinking challenge and then report how they felt. A follow up interview was conducted 10 years later
- Results: Immeditely after the drinking challenge, 40% of sons of alcoholic fathers showed low sensitivity compared to 10% of those of non alcoholic fathers. 10 years later, alcoholism was found in 43% of those who had shown low sensitivity and in only 11% fo those who had shown high sensitivity
- Conclusion: Low sensitivity contributes to alcoholism and could be partly inherited, supports genetic explanation
- Evaluation: Unethical due to involving active or recovering alcoholics. Schuckit found similar results with women
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Importance of twin studies
- MZ-share their genetic makeup and so have 100% concordancy when it comes to illnesses/ disorders/ characteristics that are caused by genetics.
- DZ-like normal siblings, they share only half of their genetic makeup however they have shared the same experinces and environments at the same ages unlike normal siblings e.g. same friendship groups, major events and the womb.
- Allows us to identify the environmental and genetic influence on the causation of the illness/ disorder/characteristics.
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- Oriental races have a genetically based sensitivity to alcohol. They respond quickly and intensely to alcohol, with a raised heart rate, nausea and flushing response.
- Have low levels of the enzyme that breaks down acetaldehyde, meaning its unpleasant side effects are more intense and last longer than normal.
- Protects them against heavy drinking- they are biologically predisposed not to drink large quantities of alcohol.
- Whilst it is difficult to conclusively show a genetic predisposition to alcoholism, we can demonstrate that people can be genetically protected against abusing alcohol
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- Twin studies- results may be due to shared environment rather than a shared genetic makeup
- Concordance rates for MZ twins- although found to be 77% in the study carried out by Mc Gue, other studies have found it to be lower e.g. 54% (Kaji). This shows an inconsistency in findings
- MZ concordance rates are not 100%- suggests factors other than gentics are involved
- Other explanations- Social influence can explain these factors that genetics is unable to, suggests that more than one explanation is needed to fully explain the cause of substance abuse
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How genetics makes you more likely to substance ab
- Certain people inherit genes that mean they metabolise ethanol differently in their body
- Ethanol breaks down into acetaldehyde when in the body, and it's this that makes a person feel nauseous and generally ill
- If an individual has a slower metabolism, acetaldehyde will remain in the body for longer, meaning more nausea ect.
- If a person inherits genes that result in a faster metabolism, they will be able to drink more for longer, makinh them at a higher risk of alcohol use
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