21.   Past cloning efforts have already demonstrated that cloned embryos are difficult to bring to term, and many that are born carry visible defects, in particular growth abnormalities.

22.   Scientists overwhelmingly oppose implanting cloned embryos in women to produce babies, called reproductive cloning.

23.   Should scientists be allowed to experiment with cloned embryos, either to create a cloned baby or to extract disease-fighting stem cells?

24.   Stem cells derived from cloned embryos would be genetically identical to the donor, which is why companies like Advanced Cell Technology are working on therapeutic cloning.

25.   Supporters argue that cloned embryos are only clumps of cells that could cure a wide range of deadly and debilitating diseases.

26.   The Advanced Cell Technology cloned human embryos grew for a few hours, long enough to form clumps of six cells, according to the company.

27.   The company announced last month that it had created the first cloned human embryos, to make tissue that might be used to treat disease.

28.   The company denied a report Monday that it was trying to create cloned human embryos and said that it had no intention of doing so.

29.   The cloned embryos would be perfect genetic matches for patients, who could then receive tissue transplants, with no need for anti-rejection drugs.

30.   The Massachusetts Democrat announced agreement with two other senators on a bill that would outlaw reproductive cloning but allow research with cloned embryos to proceed.