When researcher Irving Gottesman pooled data from many studies on schizophrenia, he found that

a. genetics had very little promise as a possible causal factor in schizophrenia.
b. if both parents suffered from schizophrenia, the probability that their offspring will have the illness was almost 100 percent.
c. the probability that identical twins will both have schizophrenia is about three times greater than the probability for fraternal twins.
d. even though there is a genetic basis to schizophrenia, the degree of genetic relatedness is not correlated with the degree of risk of suffering from the illness.

Answer: c. the probability that identical twins will both have schizophrenia is about three times greater than the probability for fraternal twins.