A photo caption accompanying a Notebook item headlined "Genetic Down Syndrome Test" (The Scientist, Nov. 24 1997, page 31) contained incorrect information. The left photo shows a single pink signal, indicating one copy of chromosome Y, which is considered normal. A double copy of that chromosome would indicate Jacob syndrome, not Down syndrome, as the caption indicated. Down syndrome is characterized by three (trisomy 21) copies of chromosome 21, which is represented by the three pink signals in the right picture.
