1.   He fears that, in the absence of federal laws, embryos will become items of trade, produced to order for stem cell experiments.

2.   It may be that embryos will become available if there are concerted efforts to encourage couples to donate them.

3.   It would become an animal that was the identical twin of the animal the embryo would have become, had it been allowed to develop.

4.   That normally occurs after about five days, when the embryo becomes a sphere with a ball of stem cells inside.

5.   The human nuclei are thought to take over the cow egg, so that the hybrid embryo quickly becomes human during the few days it lives.

6.   Malfunctioning genes can cause an embryo to become malformed, prompting the body to expel it in a miscarriage.