Final answer:
The likelihood of an identical twin developing schizophrenia is significantly influenced by different placentas, signifying that environmental factors play a crucial role alongside genetics in the manifestation of the disorder.
Step-by-step explanation:
If an identical twin has schizophrenia, the co-twin's chances of being similarly affected are only 1 in 10 if they had different placentas. This highlights the role of both genetic and environmental factors in the development of schizophrenia. Researches, such as the studies by Tienari et al. and findings from the Minnesota Study of Twins Reared Apart, suggest that while identical twins share the same genetics, environmental factors can significantly influence the likelihood of developing schizophrenia. Environmental stress and a disturbed family environment have been shown to increase the risk among genetically predisposed individuals. Additionally, antenatal exposure to severe adverse life events has also been linked to a higher risk of offspring developing schizophrenia, according to Khashan et al. (2008). Schizophrenia involves symptoms like hallucinations, delusions, and difficulty in thinking, and is thought to be related to malfunctioning dopaminergic neurons and glutamate signaling.