BREAKTHROUGH OF THE YEAR:
Human Genetic Variation

Equipped with faster, cheaper technologies for sequencing DNA and assessing variation in genomes on scales ranging from one to millions of bases, researchers are finding out how truly different we are from one another What makes us unique. Changes in the number and order of genes (A-D) add variety to the human genome. CREDIT: COMPOSITE IMAGE: K. KRAUSE/SCIENCE (HUMAN: 3D4MEDICAL.COM; CHROMOSOME: C. BICKEL/SCIENCE)













REPROGRAMMING CELLS
The riddle of Dolly the Sheep has puzzled biologists for more than a decade: What is it about the oocyte that rejuvenates the nucleus of a differentiated cell, prompting the genome to return to the embryonic state and form a new individual? This year, scientists came closer to solving that riddle. In a series of papers, researchers showed that by adding just a handful of genes to skin cells, they could reprogram those cells to look and act like embryonic stem (ES) cells. ES cells are famous for their potential to become any kind of cell in the body. But because researchers derive them from early embryos, they are also infamous for the political and ethical debates that they have sparked. New program. With the addition of four genes, human skin cells are prompted to act like embryonic stem cells.