Importantly, these chromosomally unstable hESC lines retained the canonical undifferentiated hESC phenotype (SSEA3+, SSEA4+, Tra-1-60+, Tra-1-81+, Oct3/4+, Nanog+, Rex-1+, Sox-2+), and the ability to differentiate into tissues representing the three germ layers in vivo by teratoma formation (data not shown). The gene discussed is SOX2; the disease is teratoma.