Identical twins or triplets.
Implantation.
It splits into two
implantation
Implantation
Implantation is the medical term meaning attachment of the zygote to the uterine wall. If the zygote does not attach, a period occurs.
Identical twins.
One reproductive system alone does not produce a zygote. A human zygote is made from the joining of gametes (sperm and egg) from the male and female reproductive systems.
The zygote will not implant on the uterine wall.
The answer to your question is a zygote. From there, it develops to an embryo and a foetus. Happy science!!!
Zygote
It produces a zygote.
Secondary oocyte