Full Term Development of Mouse Eggs Fertilized by a Spermatozoon Microinjected under the Zona Pellucida1

A mature motile mouse spermatozoon was microinjected under the zona pellucida of mouse eggs. Twenty-five percent of eggs were fertilized, and 54% of these developed to normal fetuses or to term after transfer to pseudopregnant recipients. These results provide a quantitative estimate of the minimum proportion of spermatozoa in a population that are able to contribute to normal development--at least 54% of mature individuals that were able to fertilize the egg after microinjection, or at least 13 1/2% (25% of 54%) of the total population of mature sperm. The production of normal young shows that sperm microinjection is a feasible means for the treatment of severe male infertility in the human and in other species.