Final answer:
The answer to the question is twins, with a 50% chance that the other twin will develop schizophrenia if one does. This reflects the genetic aspects of schizophrenia, while also acknowledging the influence of the environment, as shown by adoptee studies.
Step-by-step explanation:
The question concerns the likelihood of developing schizophrenia among family members, given that one has the disorder. According to studies, the answer is twins, specifically identical twins. If one twin has schizophrenia, there is approximatly a 50% chance that the other will also develop the disorder. This high concordance rate among identical twins suggests a strong genetic component to the risk of developing schizophrenia, albeit environmental factors are also significant as indicated by studies on adoptees.
Various studies have shown that genes and environment interact in the development of schizophrenia. For instance, adoptees with high genetic risk (biological mother having schizophrenia) displayed a significantly higher likelihood of developing the disorder if raised in a disturbed environment compared to a healthy one. Conversely, adoptees with low genetic risk had a relatively low likelihood of developing schizophrenia regardless of their environmental upbringing. This highlights the complexity of gene-environment interactions in the manifestation of schizophrenia.