Wired News: Science Makes Sex Obsolete: "In the Nov. 1, 2004, issue of the Proceedings of the National Academy of Sciences, a team led by Ralph Brinster at the University of Pennsylvania managed to grow mouse 'spermatagonial stem cells' in a dish. Also known as SSCs, they are the type of stem cells that eventually become sperm.
It gets even more interesting when you learn what Brinster did with sperm stem cells in 2001. In that study, he and his team changed the genetic program of SSCs. Because these are sex cells, any changes scientists might introduce to their genes will be carried from generation to generation. This is called a 'germ line' change, and it's a line that the majority of bioethicists agree should not be crossed, because it raises the specter of DNA eugenics.
So in theory, this technology could lead to a way to make sperm for infertile men, which most people would agree would be a great outcome. But scientists would also have the ability to alter the sperm genes so every succeeding generation would carry the change.
'SSCs provide an alternative method to modify the germ line of animals,' Brinster and his team wrote, adding that changing the soup the cells soak in could change their genetics, and 'identical or similar signaling mechanisms and culture requirements are likely to be applicable to other species,' including humans.