figure 16.5 What relatives are most similar when it comes to schizophrenia? Identical twins. They are much more likely to be concordant for schizophrenia than fraternal twins or any other pair of relatives. This indicates that genetic factors play a significant role in the development of schizophrenia (Riley, 2011). (“Concordant” means that the two relatives have the same status; if one has schizophrenia, the other does, too. “Offspring of Dual Matings” are children whose parents both have schizophrenia.)