The big day provides the perfect excuse to don a little green, prepare a St. Patrick’s Day menu, take in a parade or two, sip ...

Those kids could be identical twins—kids of the same sex developed from a single zygote that splits and forms two embryos. They could also be fraternal twins, which are developed from a separate ...

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 ...

Within hours of fertilisation, this new cell, called a zygote, divided into two identical ... the embryos create near-replicas of themselves. Identical twins. This quirk of nature has given ...