A slew of companies now offer to test your DNA and predict your risk of cancer, heart disease, and other illnesses, but can a cheek swab really forecast conditions with dozens of interacting genes behind them? This NOVA scienceNOW segment weighs that question against genetic counselors and researchers who point out how much environmental risk simply falls outside a DNA test's reach. It then turns to Harvard's Personal Genome Project, which is enlisting thousands of volunteers to post their full DNA sequences and personal health data online, a bet that open data will speed medical research even as it raises real questions about who else might access it. The second segment shifts to algae as a biofuel candidate: unlike corn ethanol, it grows on non-arable land, needs no freshwater, and doesn't compete with food crops. Scientists explain how algae strains can also be tuned to produce hydrogen, though harvesting and scaling remain unsolved engineering problems.