No, all embryos do not start as female. While all embryos begin with the potential to develop into either sex, the actual sex determination depends on the presence or absence of the Y chromosome.
Early embryos have a structure called the primordial germ cell, which has the potential to develop into either ovaries or testes.
The presence of the Y chromosome activates a gene called SRY, which triggers the development of testes.
Without the Y chromosome, the primordial germ cell develops into ovaries.
Therefore, embryos with XX chromosomes develop into females, while embryos with XY chromosomes develop into males.
