21 June 2002
Vol 296, Issue 5576

About The Cover

Cover image expansion

COVER Male germline stem cells carrying modified genes (blue), transplanted to recipient seminiferous tubules (bottom), produce rat spermatozoa (middle). These sperm can fertilize newly ovulated oocytes (top) to generate transgenic animals. How species achieve their most fundamental goal--procreation--is the focus of the special section in this issue. 2163 [Image: J. Hayden, RBP (Bio-Graphics) and R. L. Brinster]