1.   In addition, sperm no longer penetrate eggs that have been frozen and thawed.

2.   It allowed men whose sperm do not move, men whose sperm cannot penetrate an egg and men whose sperm are not even ejaculated to become fathers.

3.   The extra gene was discarded with the coat as the sperm penetrated the egg.

4.   She said the sperm must penetrate the shell for fertilization to take place.

5.   The sperm did not penetrate eggs, and conception failed.