This collection of Web sites about twins and twin biology starts with a short feature from The Straight Dope (1), which explains the phenomenon of superfecundation. Next is a more extensive piece from Scientific American (2), offering an interesting look at the role genetics may play in the chance of having fraternal twins. The following Web site contains a brief MSNBC story on the recent findings...

Created by the Biology Project at the University of Arizona, this website features an interactive Blood Types Tutorial. In addition to well-crafted problem sets, this site offers information about blood types, inheritance, and Rh factors. The problem sets for this tutorial were created by using edited versions of questions sent to the Biology Project from curious site users. The questions were...

This Web site is the online companion to Unmasking Skin, a feature article in the November 2000 issue of National Geographic Magazine, which offers an in-depth look at the body's largest organ. Visitors are invited to "go skin deep and beyond" with a photo gallery, a multimedia interview with the story's photographer, and related Web sites. The site also includes a portion of the feature article,...