find instances where one twin has schizophrenia and look to see if the other twin develops schizophrenia. look at concordance rates of this and see whether the concordance rates differ with monozygotic and dizygotic twins.
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What can be assumed if the concordance rate is higher for monozygotic twins?
that there is a genetic cause of schizophrenia
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Gottesman
gottesman found a 50% concordance rate for monozygotic twins and a 15% for dizygotic
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Testing
twins are tested to ensure they are genetically identical
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Adoption
sometimes twins are separately adopted and so if one twin develops schizo but not the other we can say that there are environmental causes of the disorder. if they both develop schizophrenia we can assume there is a genetic link.
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STRENGTH: only solution
best way to study genetic links of schizophrenia as they are the only group of humans that share either 50% or 100% of their DNA
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STRENGTH: control
natural control over situational variables/environment as the twins are reared together so have the exact same environment/likely to be treated the same
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WEAKNESS: sample
small sample sizes available: rare to find twins with schizophrenia and also twins are typically adopted as a pair not separately. not generalisable
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WEAKNESS: same environment
cannot separate environmental causes from genetic causes in cases when they are reared together as they share the exact same environment
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What can be assumed if the concordance rate is higher for monozygotic twins?
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