The past few years have seen many changes in the field of genetics, including the ability to genetically clone mammals, first achieved in 1997 with a sheep named Dolly. Still a relatively new phenomenon, news stories are continually detailing new advances in cloning, reasons why cloning is important, and concerns about the safety and ethics of cloning. This week's Topic In Depth highlights some recent news articles and Web sites that address the topic of animal cloning. The first site is a recent article from the Washington Post about the sheep named Dolly, the world's first cloned mammal, who has developed arthritis at a relatively young age and has caused some to question whether cloning can have adverse health effects. An ABC news.com article details the recent birth of five cloned piglets whose parent had been genetically engineered to remove a gene that causes human bodies to reject transplanted animal organs. An Associated Press article discusses some concerns raised by scientists and ethicists surrounding the idea of xenotransplantation (animal to human transplantation). For users who need a primer on what exactly cloning means and why it is done, check out the Cloning Fact Sheet. Developed by the Human Genome Project, it provides short, non-technical explanations of the different types of cloning and some links to other cloning related Web sites. Those users looking for more detailed information about cloning technology will find the next two sites interesting. PPL Therapeutics, which created the five piglets and collaborated with the Roslin Institute to clone Dolly, provides news articles and technical descriptions of cloning and related genetic technology. The Pharmaceutical Research and Manufacturers of America's Web site provides links to a tremendous amount of information surrounding all aspects of cloning, including recent congressional activity, news, and general resources. Although focused more heavily on human cloning, The American Journal of Bioethics Online has a Web page with links to various articles relating to the ethical issues involved with cloning and genetics.