Harvard University
Harvard Medical School: History of Sickle Cell Disease
This site is put out by a professor of the Harvard Medical School. It contains factual information on Sickle Cell Disease and the information is set up by links under different subject headings. This is a great site to check out on the...
CK-12 Foundation
Ck 12: Biology: Natural Selection
[Free Registration/Login may be required to access all resource tools.] Describes how natural selection changes allele frequency.