The heart beats in a mouse embryo grown with stem cells made from blood. Now the research that claimed a simple acid solution could be used to create those cells has been retracted. Courtesy of Haruko Obokata hide caption

itoggle caption Courtesy of Haruko Obokata

New research could be promising for infertile men. Scientists were able to make immature sperm cells from skin cells. Their next challenge is to make that sperm viable. iStockphoto hide caption

itoggle caption iStockphoto

A cross-section of skeletal muscle in this light micrograph shows the individual, parallel muscle fibers (red). These fibers work in concert to power movement. Thomas Deerinck, NCMIR/ScienceSource hide caption

itoggle caption Thomas Deerinck, NCMIR/ScienceSource

This mouse egg (top) is being injected with genetic material from an adult cell to ultimately create an embryo — and, eventually, embryonic stem cells. The process has been difficult to do with human cells. James King-Holmes/Science Source hide caption

itoggle caption James King-Holmes/Science Source

Ryoji Noyori, a Nobel Prize-winning chemist and president of Japan's prestigious RIKEN research institute, bows at a news conference in Tokyo Tuesday to apologize for the scientific misconduct of a RIKEN colleague. Eugene Hoshiko/AP hide caption

itoggle caption Eugene Hoshiko/AP

A mouse embryo grows from stem cells made by stressing blood cells with acid. The blood cells are tagged with a protein that creates green light. Courtesy of Haruko Obokata hide caption

itoggle caption Courtesy of Haruko Obokata

Maybe someday Jerry won't be laughing at George's follicularly challenged scalp. But despite scientific advances there's still no cure for baldness. NBC/NBC via Getty Images hide caption

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"Liver buds" grow in petri dishes. The rudimentary organs are about 5 mm wide, or half the height of a classic Lego block. Courtesy of Takanori Takebe/Yokohama City University Graduate School of Medicine hide caption

itoggle caption Courtesy of Takanori Takebe/Yokohama City University Graduate School of Medicine

After President Obama overturned Bush-era policy restricting federal funding of embryonic stem cell research in 2009, Nebraska Right to Life led a protest of the research outside the University of Nebraska regents' meeting. Nati Harnik/AP hide caption

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Human embryos grow in a petri dish two days after scientists in Oregon cloned them from a donor's skin cell. http://www.flickr.com/photos/ohsunews/8726915230/in/photostream//Courtesy of OHSU Photos hide caption

itoggle caption http://www.flickr.com/photos/ohsunews/8726915230/in/photostream//Courtesy of OHSU Photos

A scientist removes the nucleus from a human egg using a pipette. This is the first step to making personalized embryonic stem cells. Courtesy of OHSU Photos hide caption

itoggle caption Courtesy of OHSU Photos

Shinya Yamanaka from Kyoto University was named the winner of the Nobel Prize in Physiology or Medicine for discovering how mature, adult cells can be reprogrammed into immature stem cells. Shizuo Kambayashi/Associated Press hide caption

itoggle caption Shizuo Kambayashi/Associated Press