Can two embryo come from one egg?

Here's why:

* One egg, one sperm: Each egg cell contains a single set of chromosomes. Fertilization happens when a single sperm cell penetrates and fuses with an egg. This creates a single cell called a zygote, containing a complete set of chromosomes (half from the mother, half from the father).

* Division, not multiplication: The zygote then begins to divide rapidly, creating a ball of cells. These cells eventually differentiate and develop into a complete embryo. There's no mechanism for a single egg to split into two separate embryos after fertilization.

However:

* Identical twins: There is a way for twins to come from a single egg. If the zygote splits completely in the very early stages of development, before cells have specialized, two separate embryos can form. This results in identical (monozygotic) twins, who share 100% of their DNA.

* Non-identical twins: Non-identical twins, on the other hand, arise from two separate eggs that were fertilized by two different sperm. These twins share about 50% of their DNA, just like any other siblings.

So, while two embryos can't come from one egg directly, identical twins are a unique case where a single fertilized egg gives rise to two distinct individuals.