Having a 40 year scientific background
I feel that I must make one last submission to this thread. There seems to be a mistaken belief by some that female features are the first to develop only to be morphed later to male! In the beginning weeks of a pregnancy the developing embryo is neither m nor f, it is neutral.
Some also appear to incorrectly believe, that female is the default sex. While still just a clump of cells, the developing embryo contains certain cells destined to become the precursors of the sex organs (gonads). Even though sex was predetermined during fertilization those gonadal germ cells will not become gonads (male or female) until quite some time later. This early neutral period of several weeks, could be called the "indifferent" stage because during this time embryos are indistinguishable as either m or f. Only later, will the already pre-determined sex become evident.
The eventual sexual development of those germ cells is determined by the presence or absence of a “Y“ chromosome (and the SRY gene which it contains). With a Y chromosome present, at about week 6 or 7, the germ cells are directed to begin development of sperm producing cells and hormones which will give the foetus it’s maleness. Alternately, in the absence of SRY, a gene on the X chromosomes (DAX-1 ) takes over and directs the germ cells to produce ovaries, thus giving rise to female development of the foetus.
Here’s some non-technical reading (with actual embryo photos yet!) :- http://www.baby2see.com/gender/internal_genitals.html
Be sure to click on the link to “internal genital organs” to see actual changes to development of m and f up to 20 weeks.

I feel that I must make one last submission to this thread. There seems to be a mistaken belief by some that female features are the first to develop only to be morphed later to male! In the beginning weeks of a pregnancy the developing embryo is neither m nor f, it is neutral.
Some also appear to incorrectly believe, that female is the default sex. While still just a clump of cells, the developing embryo contains certain cells destined to become the precursors of the sex organs (gonads). Even though sex was predetermined during fertilization those gonadal germ cells will not become gonads (male or female) until quite some time later. This early neutral period of several weeks, could be called the "indifferent" stage because during this time embryos are indistinguishable as either m or f. Only later, will the already pre-determined sex become evident.
The eventual sexual development of those germ cells is determined by the presence or absence of a “Y“ chromosome (and the SRY gene which it contains). With a Y chromosome present, at about week 6 or 7, the germ cells are directed to begin development of sperm producing cells and hormones which will give the foetus it’s maleness. Alternately, in the absence of SRY, a gene on the X chromosomes (DAX-1 ) takes over and directs the germ cells to produce ovaries, thus giving rise to female development of the foetus.
Here’s some non-technical reading (with actual embryo photos yet!) :- http://www.baby2see.com/gender/internal_genitals.html
Be sure to click on the link to “internal genital organs” to see actual changes to development of m and f up to 20 weeks.

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