Central to this all is a zygote, which is what’s formed after a sperm and egg have a little rendezvous. Here’s what happens. A zygote is a fertilized egg.[1]#1 It’s created when sperm meets ...

Identical twins arise from a single fertilized egg, or zygote, splitting into embryos with duplicate DNA, but what causes the split remains unknown. Zygote splitting was once thought ...

Here's why. Identical twins (also called monozygotic or MZ twins) are conceived when a single sperm fertilizes a single egg and the resulting zygote divides in two. Because the zygote originated ...