and the final challenge of penetrating the egg itself which is encased in a protective layer called the zona pellucida. Only a few hundred lucky sperm actually make it close to the egg.

In nature, the zona pellucida, as this shell is known, protects the egg as it travels down the fallopian tube on its way to the uterus; it also regulates fertilization so that only a single sperm ...

In a study of early embryonic development in primates, an international research team under the leadership of Berthold ...