The second most frequently mutated tumor suppressor in human cancers is PTEN. The study of pten in zebrafish is more complex since following a whole genome duplication that has occurred in the teleost genomes, zebrafish has retained two gene copies of pten in its genome, ptena and ptenb. However, mutations in both of these genes have been identified by TILLING [61]. The gene discussed is PTEN; the disease is cancer.