No, that is not true. The sex of humans is determined from fertilization, that is, as soon as it becomes a zygote: if it is XX, it will be a female, while, if it is XY, a male. However, at the beginning, human embryos have the precursors of both female and male gonads.
Taking this into account, if there is no Y chromosome, the embryo will proceed with the development of Müllerian ducts (which give rise to the ovaries). Also, when there is no Y chromosome, the embryo lacks the SRY region: the sex determining region.
To sum up: it is true that one could say that, in mammals, the initial plan for all embryos is female, which is only altered if the SRY region is present.
Read the full article on: What’s the Difference Between Zygote, Embryo & Fetus? ( 33).
Andrea Rodrigo
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics.
