It May Lead to Non-Hormonal Contraception : ScienceAlert
In all of medical history, there are only two known cases of 'semi-identical twins' where two separate sperm wriggled their way into a single egg before the embryo split in two.
That rarity shows just how many defenses a human egg deploys, almost always successfully, to stop more than one sperm breaking through its outer coat.
A new study reveals in greater detail how one of those defenses occurs: with rapid molecular changes to a membrane protein called ZP2.
"It was known that ZP2 is cleaved after the first sperm has…