Final answer:
The concordance rate for schizophrenia among identical twins is 50%, while among fraternal twins it is 9%. This suggests a strong genetic component in the development of schizophrenia.
Step-by-step explanation:
The concordance rate for schizophrenia among identical twins is 50%; among fraternal twins, it is 9%.
In a 2004 study by Tienari and colleagues, adoptees whose biological mothers had schizophrenia and who had been raised in a disturbed family environment were much more likely to develop schizophrenia or another psychotic disorder than were any of the other groups in the study.
These findings suggest a strong genetic component in the development of schizophrenia, as the concordance rate is much higher among identical twins who have 100% genetic similarity compared to fraternal twins who only have 50% genetic similarity.