Great citation! But embryos aren't all XY or XX. XO (Turner Syndrome), XXY (Klinefelter Syndrome), XYY (Double Y Syndrome), and XXX (Trisomy X) embryos are all viable and produce healthy functioning adults with varying sexual phenotypes. Intersex can and does begin at conception. Biological fact.

Yes I realize embryos come in various phenotypes. I was hoping this article might help the conversation around embryos development timeline. No where does it refer to the Y chromosome “developing” later which someone on the thread was saying.

It (or they if XYY) are present from fertilization.

Of course not. It/they are present from conception. Expression of genes in the sex determining region (SRY) weeks into development initiates the male developmental pathway. But SRY mutations or other downstream gene mutations can still yield intersex phenotypes.

Um, she didn’t mention phenotypes, she mentioned genotypes. Do you not know the difference?

Thanks for posting! Sent the link to myself to read later. One of the most interesting classes I had in my senior year of college was an endocrinology class, back in 1980. And I remember this description in the textbook we used.

I loved embryology class! But my favorite was entomology, maybe I was stuck in the E’s.