As can be seen from the graph below, schizophrenia definitely has a very significant genetic component. Those who have a third degree relative with schizophrenia are twice as likely to develop schizophrenia as those in the general population. Those with a second degree relative have a several-fold higher incidence of schizophrenia than the general population, and first degree relatives have an incidence of schizophrenia an order of magnitude higher than the general populace.
The causes of schizophrenia are not fully known. However, it appears that schizophrenia usually results from a complex interaction between genetic and environmental factors. Schizophrenia has a strong hereditary component. Individuals with a first-degree relative (parent or sibling) who has schizophrenia have a 10 percent chance of developing the disorder, as opposed to the 1 percent chance of the general population. But schizophrenia is only influenced by genetics, not determined by it. While schizophrenia runs in families, about 60% of schizophrenics have no family members with the disorder. Furthermore, individuals who are genetically predisposed to schizophrenia don’t always develop the disease, which shows that biology is not destiny.
Unlike other genetic conditions such as Huntington's or cystic fibrosis, it is believed that no one single gene causes the disease by itself but rather that several genes are associated with an increased risk of schizophrenia. While schizophrenia occurs in one percent of the general population, having a history of family psychosis greatly increases the risk. Schizophrenia occurs at roughly ten percent of people who have a first-degree relative with the disorder, i.e., a parent or sibling. However, the highest risk occurs when an identical twin is diagnosed with schizophrenia. The unaffected twin has a roughly 50 percent chance of developing the disorder. The genetic component appears to extend beyond family environment. For example, children with a parent living with schizophrenia who were put up for early adoption still develop schizophrenia at a higher rate than the rest of the of the population.
Further down the page, the US government weighs in:
Scientists have long known that schizophrenia runs in families. The illness occurs in 1 percent of the general population, but it occurs in 10 percent of people who have a first-degree relative with the disorder, such as a parent, brother, or sister. People who have second-degree relatives (aunts, uncles, grandparents, or cousins) with the disease also develop schizophrenia more often than the general population. The risk is highest for an identical twin of a person with schizophrenia. He or she has a 40 to 65 percent chance of developing the disorder. We inherit our genes from both parents. Scientists believe several genes are associated with an increased risk of schizophrenia, but that no gene causes the disease by itself.16 In fact, recent research has found that people with schizophrenia tend to have higher rates of rare genetic mutations. These genetic differences involve hundreds of different genes and probably disrupt brain development.
Some of those links include actual cites from scientific studies, by the way. I'm not going to bother locating physical copies of those journals and don't have a pubmed subscription, but you're welcome to look them up if you'd like.