Research regarding the possible genetic bases of schizophrenia reveals that __________.

A) the concordance rate is higher for identical twins than for fraternal twins
B) children born of schizophrenic mothers and adopted by nonschizophrenic mothers are more likely to be schizophrenic than adopted children of nonschizophrenic mothers
C) the incidence of schizophrenia increases the more closely one is related to a schizophrenic individual
D) all of the above

All three statements are accurate and supported by research. The concordance rate (the likelihood that both twins will have schizophrenia) is higher for identical twins than for fraternal twins, indicating a genetic basis. Children born of schizophrenic mothers have a higher likelihood of schizophrenia even if they are adopted by nonschizophrenic mothers, indicating a genetic component that is not solely linked to environmental factors. The incidence of schizophrenia increases the closer one is to a schizophrenic individual, further supporting a genetic basis.