1.   Dr. Barry Zirkin, a reproductive biologist at Johns Hopkins University in Baltimore, is less sanguine.

2.   Dr. Lee Silver, a mouse geneticist and reproductive biologist at Princeton University, described the speed at which the cloning progressed as breathtaking.

3.   What he wanted to do was clone, disregarding the prevailing view among reproductive biologists that mice would be the most difficult of all mammals to clone.

4.   However, reproductive biologists are highly skeptical.

5.   However, reproductive biologists were highly skeptical of plans to clone the Tasmanian tiger, or thylacine.