This microscope image provided by Osaka University and the Research Institute of Molecular Pathology in October 2024, shows mouse eggs, marked in red and green, and sperm, marked in blue. (Yonggang Lu/Osaka University/IMP via AP)

This microscope image provided by the Research Institute of Molecular Pathology in October 2024, shows human sperm. (IMP via AP)

This microscope image provided by Osaka University and the Research Institute of Molecular Pathology in October 2024, shows the fertilization of a mouse egg marked in red and green. DNA is marked in blue, showing in the egg at the top and in a sperm cell at the bottom left. (Yonggang Lu/Osaka University/IMP via AP)

This electron microscope image provided by the Research Institute of Molecular Pathology in October 2024, shows a zebrafish sperm bound to the sperm-entry site of a zebrafish egg. (IMP via AP)

This microscope image provided by the Research Institute of Molecular Pathology in October 2024, shows the fertilization of a zebrafish (Danio rerio) egg by a sperm, marked in orange. (IMP via AP)