Understanding the Immune System: Information provided by the National Cancer Institute and the National Institute of Allergy and Infectious Diseases:
http://rex.nci.nih.gov/PATIENTS/INFO_TEACHER/bookshelf/NIH_immune/index.html

In-depth treatment of transposable elements:
http://opbs.okstate.edu/~melcher/MG/MGW3/MG322.html

Translocation exercise:
http://raven.umnh.utah.edu/units/karyotyping/translocation.html

National Down Syndrome Society Website:
http://www.ndss.org/