• Cracking Mental Illness: Researchers identified particular genes that reliably increase one's risk of inherited disorders, such as schizophrenia, depression and bipolar disorder. Understanding the underlying brain functions behind mental illness will help researchers to design more effective clinical treatments.
  
• Spontaneous Sperm and Egg Cells: The discovery that mouse embryonic stem cells can develop into both sperm and eggs may help scientists learn how these sex cells develop and why some kinds of infertility arise. The possibility that human embryonic stem cells might become a source for both medical cures and human eggs also raised complex ethical issues.
  
• Breakthrough Cancer Therapies: In June 2003, researchers announced an anti-angiogenesis drug, given with conventional chemotherapy drugs in a large clinical trial, prolonged the lives of patients with advanced colon cancer. Roughly 60 anti-angiogenesis drugs currently are in clinical trials against a wide variety of cancers.
  
• The Self-Reliant Y Chromosome: The genetic sequence of the human male Y chromosome revealed why this loner chromosome doesn't need a partner. It has duplicate genes, arranged as mirror-image "palindromes." Thus, when mutations arise and a new gene copy is needed, a twin copy is on-hand.
  
• Climate Change Impacts: No longer an abstract concept, scientists reported melting ice, droughts, decreased plant productivity, and altered plant and animal behavior as visible evidence of global warming.
  
• RNA Advances: Scientists explored how small RNAs, Science's breakthrough of 2002, impact a cell's behavior, from early development to gene expression. Harnessing the power of "small interfering RNAs" may help researchers combat diseases such as HIV/AIDS and hepatitis by controlling specific protein production.
  
• Zooming in on Single Molecules: New collaborations between biologists and physicists captured the activities of individual molecules inside cells. Research this year offered a look at molecular motors, colored nanocrystal tags attached to cell receptors and a single enzyme digesting DNA.
  
• Left-Handed Materials: After two years of debate, several research teams confirmed certain high-tech materials could bend light and other electromagnetic radiation in the "wrong" direction. Scientists used this new class of materials to produce an inverse Doppler Effect and also are working to craft better lenses.
  
• Starbursts and Gamma Rays: Scientists furthered understanding of gamma ray bursts, the most energetic explosions in the universe. NASA's Swift satellite, set for launch in mid-2004, should catch gamma ray bursts at five times the rate of any previous mission.
  
• Severe acute respiratory syndrome (SARS) earned special notation in this year's awards, serving as a reminder that new infectious diseases can emerge at any time – and don't have to infect many to choke national economies. Thanks to worldwide collaboration, scientists identified the agent only five weeks after the World Health Organization sounded its global alarm.

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