So what scientists have been doing is inserting human genes into mice, to produce similar genetic overdoses in their development. As I reported before, there have been partial insertions, but now a team of researchers has inserted a complete human chromosome 21 into mouse embryonic stem cells, and from those generated a line of aneuploid mice that have many of the symptoms of Down syndrome, including the heart defects. They also have problems in spatial learning and memory that have been traced back to defects in long-term potentiation in the central nervous system.
These mice are a tool to help us understand a debilitating human problem.
George W. Bush would like to make them illegal.