Final answer:
The concordance rate of schizophrenia among twins is influenced by genetic and environmental factors. Adoptees with high genetic risk and raised in a disturbed family environment were more likely to develop schizophrenia.
Step-by-step explanation:
The concordance rate of schizophrenia among twins is influenced by genetic and environmental factors. According to a study by Tienari et al. (2004), adoptees with a high genetic risk (biological mothers with schizophrenia) had a higher likelihood of developing schizophrenia if they were raised in a disturbed family environment compared to those raised in a healthy family environment. On the other hand, adoptees with a low genetic risk (mothers without schizophrenia) had a lower likelihood of developing schizophrenia, regardless of their family environment.