Final answer:
When identical twins share a single placenta, their chances of being similarly affected by schizophrenia are dramatically increased.
Step-by-step explanation:
When identical twins share a single placenta instead of having separate placentas, their chances of being similarly affected by schizophrenia are dramatically increased. This is because schizophrenia has a strong genetic component, and when twins share a placenta, they also share more genetic material and are more likely to inherit the same genetic predispositions for the disorder.
There have been numerous studies, such as the Minnesota Study of Twins Reared Apart and the study by Tienari and colleagues, that have shown the increased risk of schizophrenia in twins.
It is important to note that while identical twins have a higher chance of being similarly affected by schizophrenia, it is not a guaranteed outcome. Environmental factors and individual experiences also play a role in the development of the disorder.